Hi, new here, but I hear you guys really know your stuff, so here goes:

Somebody told me, "It's intuitively obvious and self-evident that gear that specs transparently will have no sound of its own, and thus will sound the same as all other transparently spec'd gear.".

I'm a little skeptical. Does this sound right and does this guy sound like he kows what he's talking about?

Well, if all distortion products are under -110dB full scale for a standard audio system, you can say that, I think, quite safely.

Things like SNR are "mostly useless" though. I can contrive (yes, these are extrema) a signal for which an added signal 5.5dB down will be inaudible, leading to at least one signal for which an SNR of 5.5dB is transparent. (This would be the classical noise masking tone in a critical band experiment)

I can also contrive a signal (19kHz full scale minus a few), with a 2 kHz added signal 80 dB down, and the added tone 80dB down will be obvious, so 80 dB is at the other end, give or take.

-110dBFS seems like very low level. What kind of equipment actually has that sort of specifications?

Exactly my point.