I'm glad we could bring back this thread which was on its way to oblivion because it is an interesting topic.
Ar_t, maybe I didn't understand your question. I was refering to filtering the HF switching noise the amp itself produces.
Tvad, even the original distortion specs you mention are ridiculously low and probably people wonder how can audiophiles argue over such tiny changes in distortion. The actual printed graphs in Fig 2 however look a lot worse than numbers on a page.
Probably the worst Pioneer receiver is 75% accurate and the best Halcro is 90% accurate so any differences are small on an absolute scale. Nothing is perfectly accurate and you make a choice based on 1) your overall system, 2) preferences, and 3) what you find objectionable.
So if tpk123 is making a buying decision, then the objective is to weed out "bad" products, however small the differences, and buy the right product based on 1), 2), 3).
When I had the PS Audio, it gave me headaches like when I listen to CD's from the Cranberries. Could've been my system, room, CD's, or ears, but it didn't sound as good as "analog" S.S. amps IMS.
Even if they can filter out the HF noise, I'd rather not have a filter used at all. One more component in the chain to mess up the sound.