It always amazes me how so many audiophiles are blind to expectation bias, confirmation bias, and ignore the well known and researched aspects of how we hear and perceive sound - i.e. psycho-acoustics.
As far as I know, the Richard Clark amplifier challenge still stands - and no one has won the money - a comfy $10k
Better yet is the James Randi challenge - the sacred cow of cables. Here you can win 1 million dollars if you can prove that mega expensive cables sound better than relatively 'normal' Monster cables. Again, no-one has won the money.
I've personally dallied with different cables - construction and cost - and was quite sure I heard noticeable differences. But as soon as I introduced some sort of control - either getting a friend to change the cables so I was 'blind', or even sighted, listening on my own, but using an good SPL meter to precisely match volume levels - and the differences previously noted pretty much went away.
A telling comment I heard recently in conversation with an audiophile who had spent mega bucks on his kit and 'accessories' at a HiFi show I attended, in the B&O room auditioning the Beolab 90's, was that he had been a fervent believer in such things, until he put himself to the test and underwent a controlled test at matched volume levels and realised he could hear no difference.
A moment of great epiphany for him - he was seriously considering selling up all his previously 'amazing' kit and heading in the direction of a pair of Lab 90s.
And so it goes. I thought my Naim kit would absolutely wipe the face off the Sony AV amp I bought - but at matched volume levels and with some blind tests aided by friends, it was not the case.
Yes, there were some slight sonic differences, as the two were very different amplifiers in terms of design, but at matched volume levels they sounded far more alike than different. By far the biggest difference was the price....
So my point is that Naim is very good. Without question. However, don't think that by spending huge amounts of money you are going to get something hugely better, or for that matter spending far less, that you are going to get something vastly inferior.
With amplifiers, you will likely at best, given similar design, power and distortion figures, and provided you are not driving it into distortion, encounter subtle nuances in sound that will only be apparent in very well known recordings; "oh, the cymbal on that 30 sec part of the recording is clearer; oh, the bass is just that little bit better defined on that 32' organ stop."
Play unfamiliar material and especially at matched volume levels and it will be very difficult to hear differences at all. That is not to say that difference don't exist, but rather they are so subtle under controlled listening to not be an issue for any sensible audiophile.
And lastly, even moving your speakers a few centimetres further apart, or away from the back wall, or corner, of moving you listening seat in the context of the listening room, or room treatments themselves, will all affect/alter the sound far more than any obsessing with cables and racks, let alone swapping out amplifiers.
Call me stupid, berate me for not being a 'dyed in the wool' audiophile, lol.. but, I've been there, and done that, which is why I've personally forsaken the hit and miss, trial and error method of system building mixing and matching with separates, and gone fully active from a one make solution.
Of course that's not going to suit a hobbyist who likes mixing and matching and tweaking, and I have no wish to denigrate that experience - but again after having been there, and done that, I much prefer the fully active route, speaking purely personally of course.
And as such, for the Naim owner wishing to move to something else, I could scarcely not recommend a fully active system (insert your brand of choice) highly enough.