Bass leaves after amp warms up?

I had the same problem with Bryston amp ...

So it would seem that the problem is most likely unrelated to the amp, and that it is related to something else that is occurring during that hour.

Does the same thing happen whether or not the CD player is spinning a CD during that hour?

Does the same thing happen whether you are listening to vinyl or to CDs (I see in your system description that you have a turntable in your rig)?

Does the same thing happen if you are not playing music during that hour, so that the speaker drivers are not being warmed up/loosened up during that time?

Regards,
-- Al

Okay fish, you're a professional musician. You've dismissed all ideas and suggestions out of hand. I guess you're on your own. Good luck and I hope the bass just mysteriously reappears for you.

Yes this phenomena happens with Vinyl or CD source
I believe wheather it's spinning or not the sound changes after the amp is on about an hour or less.
Also if I change source from CD to vinyl the sound frequently changes for the worse faster.As if I've distrubted the circut

All amps are no perfectly efficient and produce heat as a result. If the heat produced is not dissipated and temperatures rise to much accordingly, I would expect sound quality can be affected.

CAn't say why this might be occurring in the OPs case, but better ventilation around the amp, maybe even use of external fans, might help.

Based on specs the amp should be largely up to the task of driving the PSBs, but driving most speakers to very high volumes might tax most any smaller integrated amp I have seen to some extent.

I had a Musical Fidelity A3CR power amp that I believe was heavily biased to Class A and was of modest size yet quite heavy and tended to run quite hot accordingly. Might be a similar case here. I moved to a very efficient Class D amp that never breaks a sweat regardless of volume with my lesser efficient OHM speakers. Bass and dynamics is never an issue these days at any volume.

What about my third question? If, after the system has been unused for a period of time that is typical of your listening habits, you turn the amp on, play no music for the first hour, and then start to play music, what does it sound like?

Regards,
-- Al