Bass leaves after amp warms up?

Fish,

Can't you get your dealer who sold you the amp and/or speakers to help you sort through things?

You have a nice published resource here in this thread for reference, with feedback from various knowledgeable members, to help them help you sort through things and cut to the chase, which in my opinion means as a next step being able to try an amp that is better suited to drive the speakers on paper WITHOUT ANY QUESTION BASED ON KNOWN/PUBLISHED AMP SPECS/MEASUREMENTS.

Here are the things ruled out:
speakers
amps (3 amps used, from 60 to 200 watts/channel)
hearing
electrical

The only clues are: bass might come back on its own or when messing with speaker cables.

This points to another component. What happens if you listen to an LP, and not only have the digital off but entirely disconnected, even unplugged from the wall. This is sounding more like an RF interference problem, and malfunctioning digital can do that.

Atmas,

WHy rule out the amps when there is nothing indicating any of them are/were up to the task of driving the load of the PSBs without running out of gas.

RF from digital, malfunctioning or otherwise, might have an effect but my experience with that is effects are noticeable from the start and not cumulative over time. Not to say any listener might notice ANY negative effect more so over time in general.

Regardless, testing with a different source to see if same results if possible would be worthwhile.

Can't you get your dealer who sold you the amp and/or speakers to help you sort through things?

My dealer thinks I'm a kook or have hearing/mental issues..
The support @ PSB are even worse & dismissive.
I would say for the record they are rude with no patience,interest or respect
That was my experience with PSB phone support.
I would never recommened this brand to anyone even though I like their speakers..

Here's an additional thought for the OP to consider:

In my experience as an electrical engineer, when a baffling problem occurs that defies diagnosis by the usual methods, including substitution of relevant hardware, it often turns out that TWO problems are present at the same time, both of which happen to produce similar symptoms.

Not sure what this might mean in this particular situation, but it's something to keep in mind.

Regards,
-- Al