Bass leaves after amp warms up?

High damping factor for perfect speaker control
What does this mean?

listed under features of amp I'm about to audition

Damping factor is speaker input impedance/amp output impedance. High damping factor means lower amp output impedance. Amps with high damping factor are better able to control driver movement, when needed. Some speakers will benefit more than others. In general this should help produce a clean, detailed articulate bass as opposed to one that is less controlled, looser sounding, or possibly muddy. This will likely be of benefit with more full range speakers like the PSBs that tend towards lower impedance in the bass frequencies. Amp damping factor can be a significant factor in how one amp might sound compared to another.

"When I let the Accustic Arts have a go at the 87dB/4-ohm Walsh 4.5Mk II -- a speaker more in line with the amp's 190-watt delivery into such a load -- it was late in the Power 1's stay yet it gave me more of the same. While I doubt that the Power 1 will be confused with any of the mega-watt bruisers, bass through the Ohms came across as properly linear, nicely detailed and, again, very much in control. No matter what the speaker, the Power 1's bass remained highly damped and well handled. My Ohms are still breaking in and though not quite the most transparent speaker I have in the house, the Accustic Arts amplifier held up its end of the midrange bargain with smoothly flowing detail and true instrumental timbres."

My guess is the bass performance to expect with the PSBs should be somewhat along these lines. John Potis, the guy who reviewed that amp on Six Moons, was one of the most reliable equipment reviewers out there IMHO.

Set up AA Power 1 mk3 this evening with 2 hrs listening.
First impressions suggest it's a world class amp built to high standards/expectations.
It's difficult to know how the amp will sound after more hrs.but hope deeper bass will be apparent.
Fine acoustial tambers,clean articulate with liquid midrange.Classical sounds best so far and the phono stage is quite good.Also the headphone amp sounds excellent.Tomorrow will give further insight into the amps potential.
Looking foward to hear the amp open up more

Looks like a very nice integrated. I hope it works out.