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
The AA Power 1 mk.3 integrated is 200 watts into 8ohms
I paid $5000 new w/phono from distriubuter for a show demo open box.
I have 15 day test drive w/return option & no restock.
Although shipping both ways using fedex air w/insurance would be around $400
I chose this amp over Musical Fidelity pre/prx also Modwright KWI 200 & yamaha s2000
The amp arrives Wednesday-
I will post first impressions soon after
Fishing, definitely appears to be a very high quality integrated and I do hope this new amp works well for you, however someone has misinformed you about the power. The ratings I quoted was from the company's website.

http://www.accusticarts.com/pdf/produktblatt/power-I-mk3.pdf

Agree with Mapman, what's on paper never tells the whole story.
I'm with you Seikosha. I very seriously doubt that Fish's audio gremlins have anything to do with the amp.