Bass leaves after amp warms up?

Currently listening to Denon 1650ar cd player w/grado headphones-
I've been getting the music message this way.
I'm switching to Bryston separates w/Synchrony One's
If this don't work,options to try:
Different brand of cables than Audoquest
8ohm speakers @ Joseph audio
Differnt living situation
Thanks for everyone's patience w/numerous posts.
I've considered there may be a defect in my judgement.

Let us know results with the new amp and congratulations...
you reached 400 responses.

I've been having a similar problem, not only do I lose bass but the overall clarity drops. Sometimes my system sounds awesome other times not so much.
I believe I just found the problem, I wasn't sure if it was the amp or pre-amp so I ran the I/c directly from my Oppo to my amp. Flat sound no bass so it's the amp not pre. I wanted more volume so I reached around back & changed the input sensitivity switch, bass returned although the highs were a bit harsh. I moved the switch back & forth a few times & put it back where it was & it sounds great. Hopefully that's it & it will stay that way.
It's a McIntosh MC7270

What? Are you on the right thread?

The thread that refuses to die! Will it survive to 1,000 responses? What is the record?