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'm wondering if OP got his Brystons to run with PSBs or stuck with just headphones as he mentioned in last post a couple weeks back.
I'm thinking if the Grado headphone sound floats OPs boat, BRyston + PSB is a reasonable pairing to try. OR maybe he's just more of a headphones guy. That's a lot cheaper and easier to get right most of the time!!! :^)
I dunno, Mapman...going from 40 inch, 4 driver towers is very different than headphones.
OP is still here
I placed order for Bryston Seperates but the 2.5 amp is not available for 3 months so I cancelled..
I am going to audition Yamaha a S-2000 integreated amp from Amazon with return privilige..
Next choice will be Musical Fidelity pre/prx
After that I will get rid of Synchrony one speakers for Legacy or Joseph audio.
I currently have no amp but listening with headphones to shm-sacd recordings on Sony XA5400es