Long time lurker, this is my first post, please be kind 
I have found myself in a bit of a situation. I was very happy with my SN3/HiCap DR with NDX2/XPSDR as source. Speakers are Heritage Specials with super lumina speaker cables. I do my listening in a relatively medium size matchbox room, lightly treated. Now, I was always wondering how much better it can get down the separates rabbit hole and, as luck has it, I found an incredible deal on a 252/300/SuperCAP DR ex-demo, couple of years old if not less, from an official dealer and I went for it. The 4 boxes arrived 24 hours ago now. I followed recommendations from the multitude of threads on here to set them up, I let everything warm up for an hour or so and started playing music I know very well. The first couple of tracks I felt everything was much brighter but this has since subsided. I immediately noticed a significant amount of additional detail and clarity, I can hear deeper in the mix and make out new elements even in songs I know extremely well. However, there are two issues I am noticing that I cannot get over atm. The first one is that the soundstage has narrowed a bit, not a by a lot but noticeably so compared to the SN3. With the SN3 I was enveloped in a 3D stage, which I am now missing a bit. The second and most important issue has to do with low end speed. The combination of SN3 and my speakers was impressively fast, with incredible attack and decay speeds, which I now find is lacking. Everything is softer in the low end department with the 252/300, this is not subtle. I put the SN3 back on and verified this a couple of times. As a result I am not enjoying the music as much and I am not sure what to make of it. It is winter here and the boxes had a long journey if that makes a difference, and have only been running for 12 hours or so. However, those have definitely more than 200 hours on them so I do not know if I should expect significant changes as I run them more.
My opinion is only an opinion and I don’t know your speakers, but I would not have expected that result at all. Getting the boxes warm does make a difference, but should not take days.
Has anything else changed when you were doing things? Is it possible that you have moved the speakers a bit, perhaps changing how much one or both are toed-in towards you?
I did not move the speakers at all at first. When I noticed this issue I started moving them around a bit, thinking that the extra power of the 300 may have had an effect on room acoustics. I did not hear any low end improvement in other positions so I put them back where they were initially.
In that case, I am confused, but you can believe your ears more than opinions here (including mine).
Are the new boxes in good condition?
Yes everything is in great condition, looks like new. I was thinking that maybe I need to give the system a few days of running in the background and check back in. My SN3 has been running for months without interruption, I am not sure if it sounded as good as it sounds now when I turned it on first.
I made a similar change with my system during its upgrade. The 252/300 should be well ahead in all regards, so I’d run it 24/7 on low volume, or mute, for several weeks and see how it then sounds.
Can you share a picture of your set up?
The 252/SCDR/300DR needs to be on good quality racks. what about the Burndy, was it de-stressed before installation?
There is no way a 252/300 can sound worse than a SN3, and Naim kit needs a week after switch on from cold to sing…
I would not worry about it too much. I had a SN3 at my home with a 282/HCDR/250DR, same source, the bigger amp was easily better to my ears, even though the SN3 sounded lovely. The 202/200DR also sounded better to me than the SN3.
I have also Dynadio Focus 260 speakers, the Heritage definitely will sound better with the bigger amplifier, had that at home for demo also, fantastic speaker, but the F260 had a bit more deeper bass so stayed with the F260 (the cost of change was quite big to me) and the real reason, my cat wanted to jump on the heritage all the time, so that completely ruled it out due to the risk of it toppling.
I would let the 252 warm up for a week. If you still don’t like it, it Naim kit is always in demand, it will sell quickly.
Last but not least how is the new rig plugged into the mains? Using any mains extensions? which kind? Hope it does not have any kind of filter or surge protection? are you using Naim power line lites or Naim power lines. I have my 250DR and HCDR on Powerlines, they sound much better with them
These tiny details can make or break a system.
Which speaker cable are you using ?
Is the NDX2 set in ground not floating - the signal earth switch ?
It used to be said - with Olive equipment - that the system would take up to a month to stabilise, with ups and downs in performance along the way.
If you have a source such as an NAT tuner, just leave the system turned on and playing quietly to allow the components to settle in.
Thank you for all the replies so far. One more data point, I have now confirmed that by removing just the 252 and replacing with the SN3 as a preamp into the Supercap/300, the magic is back. So it’s really the 252 in the chain that is causing this it seems. The 252 is indeed more resolving, but the low end is loose and prat suffers significantly.
Equipment placement is not great at the moment, I have two stacks currently sitting on top of a very sturdy media unit. I am using IsoAcoustics pucks for the 252 though, and I would be surprised if this is the cause of my issue (given that the SN3 preamp in the same exact spot sounds great). I can snap some photos tomorrow. Regarding mains, I am using TibiaPlus cables for all components into a Superwiremold power strip (no switches or filters). I am using super lumina speaker cables. I have not worked the Burndy a lot, I will try to loosen it a bit better.
I suppose at this point all I can do is wait and check back in daily.
Not sure what you mean as stacked ?
The reason I posted a picture is to show how much space I kept between the various equipment
What are tibia power cables ? Have tried many cables but naim original cables work best
Powerline lite are one I would use for the supercap DR
I do hope this doesn’t mean the 252 is sitting on top of the SC?
The 252 is sitting on the furniture, and the NDX2 is sitting on top. Those are decoupled using IsoAcoustics at the moment. The power supplies are in a separate stack. This is temporary placement while I figure out whether the additional boxes are staying I suppose.
If you can, place the NDX2 somewhere else, even on the floor, to see if that changes anything.
Personally I would love to be at your level of system, it should clearly be a huge improvement in sound quality compared to the sn3 so guessing it’s setup issues that could be causing your issues.
Bit of work to do and a few things to try before you write off the new system.
Even now I always like to warm up my system before having a proper listen, usually a couple of hours and it seems to bring out the best .
Not that helpful but there is definitely something as miss somewhere in your setup.
Best of luck sorting it out, it will be worth it in the end.
Firstly the Supernait should not be under estimated I have the SN2 bare and it controls my Dynaudio speakers perfectly and having been on a Naim upgrade merry go round I’d now never swap it sometimes less is more and sometimes system synergy trumps all.
Having said that our ears and brains do get used to a certain sound and yours could just be becoming accustomed to what will probably end up being a better sound so swapping the SN3 in and out will confuse you more. Give it a little more time.
I would definitely give it at least 48 hours of warm up before judging. I recall moving my system after a major redecoration and it sounded dreadful at first. It had been powered down for some days. A few days later and all was well. I also have a 252 but with active 250DRs. With regard to set up, that will certainly have an impact but unless something is fundamentally wrong, out of phase, for instance, it should still sound much better than the SN3. Optimising set up should be the icing on the cake not a make or break issue. A bit of patience required. Hope all works out well for you.
Urm, I fear we’re into another 252 debate here - a search will reveal it’s been much discussed - from my experience the 252/300 has a tremendous soundstage, depth and insight. I’d give a little more time.
I was just about to post the same thing.
For me, what the 252 does is special, but if you’re thinking the presentation is a little laid back you probably need a 282 (or a 552). The 252 isn’t as “in your face” as some other Naim offerings but it does offer refinement, detail and nuance that some of the lower level, more “in your face” sounding amps, simply cannot match.
You have good components and speakers … give them a chance to “know” each other and let them settle down in a week or so … it will sound good by then. Your dynaudio will love the 252/300 combi. Try playing around w the placement of ur dynaudio . Toe in and see any difference.