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
I apologize if this has been asked already but how loud do you listen? Some speakers Qts (how tight or loose the bass is) can change when the voice coils get hot from playing loud, especially with music that has a lot of deep bass.
I will be most surprised if it turns out those PSBs cannot play loud without voice coils overheating. I would expect most integrated amps to start to clip well beforehand. But ya never know....
Think I discoved the reason for my bass troubles:

A while ago I confirmed with Audioqust how to connect my bi wire speakers..Was certain Alaister said Red treble,black bass/Red treble & black bass...It turns out from top down the correct way is Red Treble/black treble & Red bass/black bass..
The bass is sounding much better now..
It's hard to believe this went undected for so long.
I feel silly of course..
I'll be certain this was the source of my problem in a day or two.
Just curious. What is your point of reference in comparison to your assessment? I don't remember if it's been mentioned. If it has, why don't you go and get one of those?
Not sure of the question,a bit convuluted..
However the bass now exhibits consistent weight & depth.