Bass leaves after amp warms up?

Comparison with an amp well suited for the speakers, at least on paper, would seem to be the one thing to try with biggest upside. At a minimum, OP finds out if prime suspect, the amps ability to drive the speakers, is in fact an issue. At best, overall performance may well go up significantly and current problems would be but a memory.

I am hard pressed to imagine how power source would produce the pattern of sound deterioration over time described. Defective speaker wires might be a reasonable explanation. Replacing speaker wires with most anything else, even basic 12-14 gauge zip wire, should be enough to determine if current wires are defective in some way leading to deterioration of sound over time.

The dropout in sound as described seems to fall in line with what one would encounter if one phase of the signal/incoming power feed were to drop out somewhere along the line. Preamp volume control or ac outlet problem possibly? However, I cannot reconcile the fact that it only seems to occur after warmup with my hypothesis.

Ant
When is the electrician coming over?
Best JohnnyR

The speaker cables were already replaced with the same model *audioquest comet biwire

The problem still persists:

I am auditioning different speaker cables tomorrow followed by Electrician to check connections.

I will report back

Thanks to everyone

I substituted Different high end speaker cables today.
What I heard was alot of bass but it wasn't the lower octive & punchy kind which I get from Audioquest.
Is it possible audioquest cables can in the first hour put out a more desirable bass like a subwoofer that is punchy but then "resort" to bass that is less deep or punchy?
Which is unsatisfying to me

Perhaps I need a subwoofer?

But this is perculular:
I put back Audioquest cables using just one speaker & was unable to get the "correct" bass from either side of the amp.
I then tried the other speaker cable from audioquest & the bass was powerful & deep again.
So I don't know what this means