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
Accustic Arts/psb/sony/rega photo:
http://forum.audiogon.com/cgi-bin/fr.pl?vdone&1372392821&view
Yay, I detect a happy customer.

Wait till he see's the high priced consulting bills we're all about to send him.....

Especially Al's!
Does Accustic Arts have distribution in the US? I guess it must, but I can't seem to identify it.
Mu guess is that if you were to hook up your old MF integrated you will have no further problems with your bass. I'm sure the miswiring was the culprit (or, at least, that the MF wasn't). At any rate, a happy ending, it seems.