Lots of good suggestions above. In addition, there might be a room interaction exacerbating the problem. Excessive treble is often easier to deal with than bass issues. Room treatment such as absorbent panels may not be feasible in a shared domestic environment, but adding cushions, a thick rug, breaking up hard walls with bookshelves etc. could perhaps ameliorate the brightness enough to restore your enjoyment.
Roger
Iâd just give it longer to settle in. Then fine tune the speaker and listening positioning. Iâve also found Superlumina will balance out any brightness and result in a more refined and natural presentation.
Iâd start with trying some NACA5. I purchased some TQB2 and on my system it took away some warmth and definitely made the system leaner sounding. I just donât think the cable has a large enough sq mm area for a system like yours. Your amp will want to deliver lots of current quickly and Nac A5 has the cross sectional area to deliver it.
Is the brightness still heard as a nuisance if you stand up, move about the room, go out the room ?
If yes, than that could be a way to rule out speaker positioning and room interactions:
Instead of trying to pinpoint your troubles, you should try a process to eliminate and narrow down the possible causes.
This forum constantly amazes me.
The best advice in the thread so far is to adjust your speaker positioning, it may only need a slight adjustment but this can have a huge impact. Many here have noted over the years that upgrading components can lead to a different sonic balance which a slight change in speaker positioning can sort out.
I really think that changing interconnects ,supports, the football team you support will do very little to help your problem.
I could never really get on with the Hi-line- I found it quite a variable interconnect so if you have your basic lavender it might be worth putting this in situ to see if it has an effect.
Adams advice about the Burndies is also worth following.
Although I really am not a great believer in the rollercoasters of run ins â I thought my own 300 DR sounded pretty good immediately it was plugged in â certainly it didnât sound bad. But so many people here hear these things itâs probably best to wait a little while for further running but if this does not ameliorate your problem having tried speaker re-positioning I really think you have to consider a defect in the DRing - Iâm presuming here that your NDS and CD555 displays the same treble issue?
.sjb
The cd555 is the NDS power supplyâŚâŚcd555ps.
Can you get the speakers a little further apart to create a 2.5m triangle. A 300DR has some gusto and can drive most speakers effortlessly. You may be hearing some of that change from the 250 cm sitting that close. As the other member said, tilt the speakers to eliminate the direct line of fire to your ears, every little tweak helps. That amount of toe in may need adjustment too. I had to reposition my pmcâs after I set up my 300.
Scott
Yes. Perhaps if Miles Davis had released âkind of Greyâ instead of âkind of Blueâ
The album might well be not widely recognised as such a great album.
The once wise classical scholars of science were taught to be mindfull of the muses of the Arts. 
Missed the ps bit. One would have to suspect that there possibly is an issue with the NDS. @bitsrbits do you have another source to try?
.sjb
I owned Sopra 1âs for over a year with 272/xpsdr/250 DR. I used Naca5 with Naimâs standard interconnects.Later I upgraded to SL full loom.Unfortunately these speakers will never sound good with Led Zep or Rush. For that,look at Klipsch Heresey,or Paradigm. The S1âs excel at Jazz,folk type music,not hard rock. Many have tried,most have failed.
Thatâs certainly a matter of opinion
Agree on this but experienced with other speakers. Some speakers are madly in love with a certain genre and sound awful with another. After I stopped fighting and moved on to another speaker that was better overall but maybe not killer on something specific my love for music came back. I believe a lot of equipment in HIFI lost track of music and just focus on details and how great certain tracks can sound.
Yup, this would be my first move, before anything else.
HmmmâŚdid Quadraspire make a rack with toughened glass shelves or is this a mod youâve done yourself to replicate how the Fraim works? The reason I ask is that I played around with glass shelves on a Quadraspire and the results were pretty dire. Bright, glassy, edgy would be exactly how Iâd describe it. When I removed the glass and put the equipment back on the bamboo shelves my sanity (and sound) was restored.
Also remember that both the NDS and CDP have metal feet for specific use on a Fraim. This is likely to amplify the type of surface/material you are using. Can you remove the glass or try the bamboo shelves under these two pieces of equipment? Thatâs where Iâd put my money.
Iâve had a battle with brightness in the past but it was with Thiel speakers which are rather different to Sopras. Brightness on these centred around 5kHz and was particularly noticeable with piano music and worse with an electric piano.
Speakers adjustment, sometimes quite small ones can help. Having a step in the wall behind might make this even more sensitive.
Before you start on the speakers a little housekeeping, the Burndys have already been mentioned but itâs worth reiterating that there should be destressed and hanging free, not on the floor or tangled up with other cables or touching the wall. You can often get Burndys to cross without touching as theyâre of different stiffness and stick out further before curving down. Power cables in particular shouldnât touch the rack shelf and preferably no other cables either. Interconnects should also hang as free as possible, the Hiline particularly should clear everything.
Remember all these cables are directional and thereâs no rational explanation for it.
It might all still come to nothing and thatâs the time to look at the rack and speaker cables and by then any run in should be over.
Very true. The original Vinyl - and the Remastered CDâs - are all fabulousâŚ
Just listened to 25th anniversary edition on quboz, just to confirm we are correct. 
Also listened to Power Windows Hires, this is my favourite Rush album. When I bought the album many years ago, I was playing it on a turntable in a not very revealing system, it sounded superb. However, on a revealing system (even with a turntable) it sounds way too bright for my taste. Plenty of detail on the quboz hires, but I doubt if I could listen to the whole album.
Maybe Bit should go back to a Non DR 300; if it enables him to listen to the music he enjoys.
Of Machine Head� That is the remastered/reissue CD set that I have. One CD is a straight remaster - the other is a remix and remaster, supervised by Roger Glover. Its the 2nd one you want⌠IMHO⌠
Regarding general âbrightnessâ, I would say tweaking speaker position is the way to go. The worst situation should be with both speakers toe-ed in so they âfireâ straight at the listening position. Leaving them âstraightâ - back to the wall - is the other obvious option.
But⌠its not a problem I have ever had⌠
I experienced a similar problem as the OP.
I had my 300 updated to DR almost two years ago, and had the same reaction. After changing speakers & positioning, reorienting my room with speakers on opposite wall, repositioning components within my rack, I decided to send in my 252 and have my SC DRâd. They are still out, but Chris West at AV Options (Iâm in the US) found problems with my 252 and a leaked cap in my SC, so I am anxiously hoping one of those may have been the problem all along. Iâm guessing that the increased resolution of the DR upgrade resulted in hearing a problem lying elsewhere in my system, and that was not apparent with the non-DRâd 300.
I had also switched from NACA5 to Townshend ISOLDA speaker cables, which sounded superior (IMHO) to the Naim cable (I hope that last comment is permissible).
Why? There are many options and opinions, say whatever you think is right. Naim products are superior to most of the things out there, but of course they can learn from their competitors.