Gdnrbob & Bombaywalla, thanks!
I am in essential agreement with most of what has been said above. I would commend the following thread to the OP and anyone else who may be interested, in which I, Atmasphere, and others posted on the subject of amplifier specs in general and THD in particular:
https://forum.audiogon.com/discussions/amplifier-specs-does-they-matterOne of the basic points I stated in that thread was precisely what Bombaywalla said above: Specs and measurements, including THD, can often be useful in RULING OUT potential candidates for purchase from consideration, in some cases by identifying specs that may be TOO good, and thereby may signify the likelihood of undesirable design tradeoffs such as excessive use of feedback.
Personally, regarding the specific amplifiers that were cited in the OP, if I were amplifier shopping I would probably not include either one on my short list, regardless of what the reviews may have said and even if cost were no object. An amp having a 5% THD spec, no matter how euphonic and pleasing it may sound on initial audition, would over the long term cause me to unduly focus during my listening sessions on how untrue the amp is being to the recording, rather than simply enjoying the music. And an amp having vanishingly small THD would over the long term cause me to unduly focus during my listening sessions on whether it might be introducing excessive brightness, sloppy transients, and other effects that can result from heavy-handed application of feedback, or from other techniques that may have been used to achieve those numbers.
As I see it there are more than enough well regarded amps to consider, in all power ranges, that have specs that are neither "good" nor "bad" to a degree that would raise concern. Given that, I would see little point in pursuing ones having specs like these.
Regards,
-- Al