What could I expect to hear from a Class A amp?

Class A would be most evident at low power operation (less higher harmonic distortion from zero-crossing effects).

If you use highly efficient speakers that barely use one watt then I'd definitely consider Class A. If you use something a little inefficient say only 91 db SPL for 1 watt at 1 meter then you could go for a design that runs Class A up to a certain point (this kind of topology exists and is well documented - sliding bias if you will). If you are driving something very inefficient like 85 db spl then I'd probably say it is not worth it and stick to Class AB or you favortie Class D etc., as running Class A will be like adding a furnace to your house...

On the warmup issues I think one needs to be careful about making too many assumptions. Firstly a Class A amp will actually begin to cool down when you first start running it (yep, it will run cooler when you have a load). This then opens up the question what kind of load or what kind of RMS power is running through your amp during different tracks and passages of music...all to say that temperature equilibrium doesn't actually exist - it will be changing all the time (so good design is what matters most - agood design will also give the product a longer life as heat generally causes components to fail more quickly). A warm up of 5 to 10 minutes with some heavy music will actually get the major components warm pretty quick (even if the cabinet or heat sinks does not yet show it - at the component level things are already well on the way to approaching design operating temperatures).

Finally, is anyone even aware of the 150+ degree temperatures in the voice coils of your speakers? Did you know that this tempertaure is constantly varying depending on the type of music (quiet and loud passages). Ever play a song that sounds real loud at the beginning - great bass slam and then it seems to lose its punch???....well that would be thermal compressiono in your speakers and it happens in mere seconds from hot voice coils...

All to say that there are big differences in sound in the majority of speakers becuase many are not designed specifically to eliminate thermal compression (by using humongous voice coils for example - this is expensive and not immediately obvious so manufacturers do not often focus on this aspect - given that a better cabinet or better price point will be more appreciated by consumers). Not only will this affect dynamics but it will affect how well the crossover behaves, as the impedance of the individual speaker drivers drift with increasing/decreasing temperature.

If you prepared to worry about your CD/amp warm up - then you should be much more worried about your speakers!!! Ask a simple question - do they have pro drivers with large diameter voice coils? (large diameter increases surface area, which increases heat dissipation and reduces thermal compression effects)

I'm not sure I understand, though, why Class A would run cooler when outputting signal into a load. It's tempting to think that could result from a portion of the current that would otherwise flow through some of the output transistors (at zero signal conditions), being diverted through the speaker instead.

Yes that is the reason. At no load (or I meant to say no input signal) you are actually running at 50% current output and all that current has to be dissipated internally in the amp somewhere, across the bias circuit if you will (it is the high bias that makes the current flow at 50% when at zero input signal). When you play music the +ve signal requires more current (but it all dissipates in the speaker) and on the -ve cycle it actually diverts current from the bias circuit to the speaker (meaning the amp generates less heat).

The amp may use more power from the AC but it will likely run a bit cooler - no enormous difference and I gues it may vary a bit on the exact topology and type of output devices.

The usual total harmonic and intermodulation
distortion figures do not reveal the abrupt output stage distortions accurately
because of the averaging factor involved in such measurements. A spike of
crossover distortion may reach 2 per cent, but if it occurs only over 5 per cent
of the waveform, it averages out to a respectable 0.1 per cent distortion
figure.

What he doesn't say which is important is that the crossover distortion is
fixed (it is not amplified as you crank up the volume, at least that is my
understanding) - therefore Class A becomes critically important at low power
output => this is what makes designs with sliding bias or several stages that
include a Class A stage attractive. (it allows distortion to remain low at low
output levels or quiet passages but then still gives you the ooomph needed
for loud passages....the crossover distortion is less critical during a loud
passage as it is a relatively small amount on a good Class AB design
compared to a big signal output)

This also makes an active speaker topology attractive. Since the distortion is
high order then some of the worst stuff is going to come out the tweeter. In a
biamplified active speaker design you simply feed clean Class A for the feeble
power requirements of the tweeter whilst you can power the mid/woofer with
a beefy Class AB design without much worries over high order harmonics or
intermodulation distortion being all that audible

It would be nice to know of non-Pass Class A amplifiers that perform well, and why so.

ATC make amplifiers with what is probably a sliding bias - you get 2/3 power Class A before it reaches Class AB operating point for the final 1/3 power. I have not compared them to Pass but ATC are relatively unknown as an amplifier manufacturer whilst Pass is legendary. You are safe sticking with Pass, IMHO.