Pass labs xa25 amp and BW 804 d3?

Although I suspect that you would have been very likely satisfied with the Parasound A21 amplifier I believe you selected the better sounding amplifier. I’m glad you weren’t swayed by those suggesting the Pass XA25 would be under powdered for your speakers. Congratulations and I’m happy for your very successful outcome. You describe the sound quality as "spectacular" that pretty much says it all. Just think about this, sound quality will improve as hours of use accumulate. 
Charles

Well this explains Macguy's observation of his Pass Labs X250 not leaving class A operation while driving the Vandersteens, 95 db SPL is plenty loud for many listeners. Al thanks for the additional information and the always keen commentary. 
Charles 

I do understand the desire/concern of many listeners in regard to "headroom" availability for demanding musical peaks and the fear of having insufficient ’juice ’ on hand. This is a common topic in audio forums. I do think that to some extend it gets blown out of proportion. I do not agree with the popular audiophile axioms, "the more power the better" or "enough power is never enough".

I’ve read (more than a few) testimonials on various forums from those who drive their 100 db> horn speakers with 200- 300 watt amplifiers so that they "never run out of headroom" regardless of volume or music genre demands. So without any doubt there are those who have different perspectives and experiences. Speakers of this type can provide reasonable SPLs (65- 75 db C weighted) with only 1/20- 1/100 (0.05 to 0.01) of 1 watt
Charles

Macguy said his meter indicates the amplifier remains in "class A operation". So the first 20 watts of the x250 is bias in class A (bias set  at 0.8 for this model per the Nelson Pass article). At his listening levels the Vandersteen speakers aren’t demanding of more than these first 20 watts. I suspect that very often not more than a few watts are utilized at easonable listening levels.
Charles

How many class A watts does  the Pass Labs x250 provide? 
Charles 

Hi B,
If I  am among those you're referring to, I do not own  a Pass Labs amplifier. I'm  just  aware of their design objectives and the very conservative power rating method they employ. 
Charles 

Kosst_amojan,
I agree with your calculations and reasoning. This is the point I was attempting to illustrate in my prior post. You can’t look at the XA 25 and conclude, "oh, it’s just a 25 watt amplifier " . There’s considerably more going on here if one can appreciate the design/circuit and implementation. As you calculated, at very reasonable (even generous) volume levels these speakers aren’t demanding much power/ watts at all. And as a reminder, 200 watts/10 amps  (current max) into a 2 ohm load.

DF of 500 is still pretty high relatively speaking in regard to the XA 25. I agree the XA 25 and XA 30.8 are notably different circuit designs. I’ll empathize again, Parasound A 21 or one of the Pass Labs amplifiers, you have to hear them with the specific speaker of interest. Each amplifier will have its own sonic signature with a given speaker.
One point to consider regarding DF is it is inversely proportional to the output impedance (isn’t necessarily a bad thing) and the higher the DF the more NFB utilized (Which ’could’’ introduce some undesired sonic consequences of its own). Another point,  speaker sensitivity measurements are of a single speaker.  Generally 3 db is added when discussing a "pair" of speakers. 
Charles

Gweedoargus,
You have gotten some good responses and comments. I’m inclined to agree with those who have raised the very important consideration of ’sound quality ’ as compared to increased quantity (higher oower/more watts). The Pass Labs XA 25 is capable of 50 watts of pure class A into a 4 ohm load (this isn’t an insignificant amount). It can provide class AB 200 watts maximum into a 2 ohm load (This is impressive).

The John Curl designed Parasound A21 offers class AB 250 watts into 8 ohms and 400 watts into 4 ohms. So clearly higher power. I suspect it has pretty decent sound quality. Keep in my its DF (Damping factor) is >1100!! This suggests very heavy use of NFB. Some very respected amplifier builders such as Atmaspere and Roger Modjeski consider this amount of DF gratuitous and without meaningful benefit. On the other hand some builders (John Curl I’m sure) would beg to differ. My gut feeling is that the Pass XA 25 could very well be the superior sounding amplifier.

Is there the interest/desire to home audition these amplifiers and actually hear them driving your B&W speakers? I would bet that the vast majority of your listening the XAX25 would remain in class A operation. This is a good thing IMHO. I'm expressing my own biases. I don't believe in the cliche of "the more power the better" once you have sufficient power the objective should be placed on quality. 
Good luck,
Charles