Bass leaves after amp warms up?

But I think you will practically attain very high levels of performance sooner by using a dedicated amp better suited to bring out the best in the PSBs. Use the current MF integrated as a pre-amp only then, as AL suggested.

I have requested loan of MF amp from my Dealer
Still no response

I have arranged person with SPL meter to visit next week.
AP

Let's see what the SPL says. We'll all be waiting to hear.....

Fishing, You've had so much good advice here, I believe the solution lies within. I don't think you should make any major decisions (like new speakers) until you've measured the SPL.
On the subject of amps into PCs, just FYI, my Sunfire manual states "do not plug the amp into a power conditioner."

If the digital was unplugged, seems like we can rule that out as being a problem.

Go ahead and restore the system.

I realize I made a poor assumption. I would not have turned off the amplifier when messing with speaker cables. Most transistor amps don't care, and our amps don't care, so I always leave them on.

The fact that they are getting shut down is significant. As I mentioned earlier, the fact that messing with the cables gets a response is an important clue; turns out the amps were shut down during this time! They have become suspicious again.

The only bugaboo is that I think we did a test where the system was played until the bass dried up, then it was turned off for a while and restarted. The bass was still gone. But maybe it was not shut off long enough.

Next time the bass dries up, shut the entire stereo off for about an hour, then see how it sounds.

Next time the bass dries up, shut the entire stereo off for about an hour, then see how it sounds.
That's exactly what I will try
Thanks