Class D Technology

The output filter vs switching noises frequency is the bottleneck for Class-D HF distortion and low impedance drivability.

It is ill minded and made up.  There are many amps that have similar bandwidth and great reviews.  My tiny amp is listed as 3 ohms minimum and it drives 3.6 ohm min. Hyperion HPS-938 speakers.  Larger modules, like one used in mapman's amp, can drive 2 ohm (this module can deliver 40 amperes for 0.5 sec and 36 amperes for 1s - not many amps can even do that).  One of our audiogon friends uses class D amp (H20) with Apogee Scintilla in 1 ohm mode with great results.  Please stop making pseudo-scientific reasons - it is not funny anymore.

Back to the OP's question (really two questions);

So my question is, if it weren't for efficiency & power, would there be any reason to own a Class D amp? Do they beat Class A in any other categories that count for sound quality?

The obvious reasons to buy a Class D amplifier are power per dollar, efficiency, and form factor (i.e., small).    They should also work well in powered speaker implementations.  From a sound quality viewpoint, some, like Guido who posts here, have had good luck with cutting edge designs from Rowland and Stereophile certainly gushed over the Theta Prometheus that uses NC1200 modules with a linear PS.  However, even the Mola Mola that 6moons praised has received some responses that it is not quite ready to compete with the best.

Based on my singular experience with a pair of Ncore NC1200 monos, the one sound quality based reason I can think of that somebody may like Class D over (high quality) Class A is low noise.  The Ncore NC1200 amplifiers were dead nuts quiet.  My Class A Clayton amplifiers are not as quiet as the Ncores but they are certainly no noisier than other Class A and AB amps I have owned, quieter than most, and quiet enough that noise is a non-issue.  Sonically, the NC1200 amps came close to the Claytons in several respects such as having a nice tonal quality and full, powerful bass, but even in those strength areas, the Class A Claytons offer a bit more realism and enjoyment.  In some other areas, such as high frequencies and soundstaging, I find the Claytons to be clearly better.  With respect to sound quality and listening enjoyment, of the amps I have owned, I would rank the NC1200 amps about fourth.

The best reason to buy is that the good ones sound great even with harder to drive speaker loads due to lots of power and current delivery possible out of a smaller package due to efficiency.  

It sounds like a Class D amp would be best for a sub-woofer, based on a comment above

If the new MOSFET designs will be out (as products) soon, I would not want to sink too many $$ into an amp right now...

One of our audiogon friends uses class D amp (H20) with Apogee Scintilla in 1 ohm mode with great results.

Then I feel sorry for this person as he has never heard his Scintilla’s at their best. It may work, but at their best?? FAR FROM IT!
As they are a great speaker and should be driven with the right amp and Class-D is definitely, absolutely, not one of them, not yet anyway, give it some time and in the future it will be.

Cheers George