Bass leaves after amp warms up?


I don't understand-after my Musical Fidelity M6i amp warms up for about an hour I notice the deep bass & kick drum aren't the same.
They sound less musical with loss of weight/depth.The notes are there but the moving of air have left.Sound is has much less impact and boreing.
I had the same problem with Bryston amp so there is no defect with amps nor with the rest of my equipment/
PSB Synchrony one speakers,AQ cables,Bryston CD Player.
My question has anyone heard similar & is there a plausable reason?
fishing716
Hopefully the new amp is coming this week and will help pave the way out of hifi hell into utopia.
Dang, poor guy. I can't believe this thread went eight pages. I would have thought it was a joke if he hadn't tried so many fixes.

I hope you get it figured out Fisher.
"It ain't over till the fat lady sings."

..without losing the bass and dynamics! :^)