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 go back to my original assertion. As Almarg says the results suggest that these amps could not hack it with these speakers (not a good match into a 4 ohm load). I would look at trying an amp with the PSB'a that doubles its power into 4 ohms. (high current)
Can you suggest integrated amps that double it's power into 4 ohms
Not Bryston or Musical Fidelity..I'm not familar with other integrateds
Atmasphere
After enjoying the system sounding great for 2 hrs the bass dried up.
I waited 1 hr.tried again but no improvement.
Turned off amp for 1hr.returned & the presentation was still awful.
I also observed when I change source on the amp it seems to create a break in the circut & the bass leaves soon after.
I've sometime observed after turning a record around/changing channels on a cable box or changing imput buttons on the amp may upset the delicate balance.
Disregard previous post:
Makes no sense!@
But there is no pattern when system sounds optimal:
Could be am or pm