I agree….I’ve made that very upgrade and subsequently added a second 555PS which take it a good step further again.
I’m just offering the alternative view that it if the OP likes his NDS he might prefer to go 500DR first as it won’t be shown up with the upgrade in amplification.
That just goes back to my previous post in that getting the 500DR now is a large expense, and, with the OP’s 552DR, simply unbalances the OP’s system, as it would really need a ND555 to get the full benefit from the 500 amplification, so even greater expense to return balance.
If I were the OP I would stick with his current system and save to improve the source which will benefit his existing amplification IMHO.
I have the Nds / 555 dr. I have heard twice the Nd555 at dealer place, in a system I know well. I believe, it engages only me, that an Nds/ 555 dr with a PhoenixNet switch is very near from Nd555 with a standard switch.
So I am not sure that getting the Nd555 is an absolute priority, only if bought at a bargain second hand price. New, it’s 20k euros today, and the Nds is generally sold 2,5 k actually.
If the Kudos 606 will stay in the future, a 300 dr is really enough for them. I would send the 300 for dr, and buy a PhoenixNet. I had the Cisco 2960 before, the Innuos switch is another world. It greatly enhanced my Nds.
Stu,
just my two cents but at least they come from personal experience.
I have regular and frequent chances to hear a 300 and a 300DR, both with 252/SuperCap. The non-DR with Harbeth SHL5s and the DR with Focal Sopra2s. Sources are CDS3 and NDX2 respectively.
This being the Naim forum, you probably have gotten, and will get, 95% of replies favoring a DR amp. I don’t know. The 300 is one of the best amps I know and the one I’d choose if I were into Naim again and I wanted to spend such money. It’s competent, sweet, powerful and has the best bass in all Naim amps I’ve heard. I think I’d a glorious amp, and I’ve never used the word before.
Of course dealers must be helped to earn their day, but consumers have a right to be helped to spend their money wisely. An upgrade is not mandatorily an upgrade. If I had a 300, I’d keep it. But that’s just me.
As for the speakers, upgrades not being really upgrades is even more true in my opinion. Speakers are a matter of personal taste. At the end of the day I don’t love Harbeth per se, but I always find pairing them with Naim an excellent solution. With such a good amp as a 300, I’d simply go for whatever speaker turns your senses on.
Best
M
Really enjoying reading all the comments, thoughts and suggestions.
Not that you’re making this any easier for me 
I guess that’s cos they’re all great options including the ‘do nothing’…
The point about balance is really important. I’ve been there before with an unbalanced system and it sowed a nagging and persistent dissatisfaction
Stu299. Maybe you need to swap the 606 out and put back an SL2. Could that be the answer?
= Buy More Music… 
Interesting idea but I think the 606 work well in the space and also I have hollow walls
I think it’s a glorious amp - obviously.
Nigel , I came to the same conclusion in my system which was a ND555,252,300dr using T606 speakers. I had been using this for couple of years but my ND555 had problems which meant two trips to Naim H/Q my dealer leant me a NDS on the first occasion and then a NDX2.
This was the first time I had ever heard a NDS and after using a ND555 for a coupe of years I found in my system and room the ND555 was considerably better by a large margin as it should be given the price.
Having changed to a 552 last year I can imagine that these difference would have shown up even more.
How did the NDS compare to the NDX2 out of interest?
Not going to argue with that. Not one bit!
I was very impressed by the NDX2 with the 555ps but I never did a direct comparison as there was a time gap between using the NDS and NDX2 but I was really surprised at the NDX2 in my system at the time whether after changing to a 552 this would have changed my thoughts this is a difficult one to call.
Own room, own system and ears everybody hears things slightly differently.
Stu, I too think you should stick. I have gone through this process myself and my 2004 300 sounds great. It will get a service when I can but not the DR upgrade. Opening the window at the back of the system could unbalance what you have too. Just my personal solution to your question of course.
@Stu299 sorry late to this
also had the same a issue a years ago, in July 2017 I added a 300 Non DR to my then 282/HCDR main source LP12 and NDX = I was delighted with the system and moreover the 300 - soundstage, musical focus and drive, I have have always maintained the 300 is one helll of a great AMP , and for me my end game so DR upragded in Feb 2018 - if you like what the 300 does the DR upgrade IMO is a must more of everything the 300 has but just more - 300DR is a true delight and for me the DR upgrade was worth every penny
I over time added SC to 282 and then 252 with my main focus on my LP12
so as others have said on prevoius replies the ND 555 is a game changer on source, a number of my friends have moved from NDS to ND 555 and love the musical results
300 either DR or Not will drive those lovely T606 with ease and poise - I have the baby T505 due to room size
would a 300 non DR live with ND555/552 yes I certainly think so so thats one cnosideration if it was my hard earned I would go ND 555 with 300DR rather than 500DR with NDS
not sure I have answered your question ? but enjoy the music
Sure why not go ahead and get the DR300 and have “more of everything”.
Then go for a 500 and have “even more of everything”
And you still have the option to DR the 500 to get “even more of even more of everything”.
And then perhaps you may feel that you don’t know what you’re missing so there is always the statement which apparently gives “even more of even more of even more of everything” and at this stage if you still think you might be missing something then perhaps you are.
Two roads diverged in narrow wood……
.sjb
Thanks all, it’s given me plenty to chew on.
Right now I’m erring towards a 300DR. Reasoning as follows:-
But then again, if an affordable 500 comes up who knows…
Do you have already Superlumina interconnects ?
No just the regular Naim out of the box cables…
Can’t you try one before committing?
Seems to me that you have that incurable itch that you think needs scratching. If you are happy why not leave well alone and save the money for the proverbial rainy day or just do something else with it.