The speakers may be the point of the changes.
I have noticed the effect slightly prior to my current setup, but never to this extent.
I would have to hook up some other speakers to the amp so it can stay on, and the Magnepans not powered, then swap them back quickly, to judge if it is the speakers, or not.
(I have other small speakers which could be put onthe amp to leave it on. the thing i would want to be able to turn off the amp and back on within a few seconds, so banana connections would be required, for speed.
I might be able to make up some just for the testing, but it (being my slow and lazy self) may take awhile, or not.
I have the banana connectors laying around. and some wire.
The current wires are bare ended at the amp, sticking bananas on them is not a problem, then adding a wire to the spare Canton CD300s no problem either. Just have to do it. Then it would be off at pre, switch off at amp. pull banana, stick in other banana , amp switch, pre switch back on is like under ten seconds.
So the test would see if the speakers are the problem being cold, and the amp was left on. Or if the sound is great, then the amp cold was the issue.
At least one other person said they noted something like this, so i do not feel so out there (in the other thread about this issue)
It is like trying to sail against the wind, in a 'Bryston is perfect how dare you speak against it' sort of way.