Bass leaves after amp warms up?

"Clearly we're making progress"

What progress have you made? I'm not seeing it. If you have an audio dealer close by I suggest trying a different speaker. Maybe your favorite stereo store will loan you a demo speaker. I have a feeling this problem will go away with another speaker.

I had a similar problem with a pair of Ruark Talisman speaker. I was driving them with a pair of Dynaco MKIII monos. After the system warmed up the sound became too lean. I replaced the Ruarks with Living Voice Auditorium speakers and the problem never revealed itself again.

Fishing716. What I believe is happening is that when the amp is cold the bias is naturaly low, this does not tax the power supply as much as when the amp has warmed up, and the bias is at it's max adjusted setting.
However if the power supply is not up to the task it will sag on bass transients more when the amp is warmed up than when it's cold. As the bias is asking for more current when it's warm than when it's cold.

Cheers George

Quiescent current is higher when the amp is cold and decreases as it heats up whether the outputs are mosfets or bi-polar. But more so with mosfets than with bi-polar outputs.

You're right I haven't made any progress
The problem persists

I didn't expect to have a problem with such high end equipment.
Apparently what you say about the amp seems to be happening:

"if the power supply is not up to the task it will sag on bass transients more when the amp is warmed up than when it's cold. As the bias is asking for more current when it's warm than when it's cold".

I should either change speakers or amp right?

"I didn't expect to have a problem with such high end equipment."

Now that's funny.

It is my understanding you have tried more than one amplifier. So, you think the power supply is sagging on all of the amplifiers you tried with identical results?