Are Pass Labs amps probably the best ever you can buy ?

Ayre >>>>>> Pass
Everyone else is wrong.

OP, if you have $15k for only the amp(s), then you should consider the GaN-FET class D amps from AGD Production, Vivace monoblocks. They are $15 per pair. Here is their URL link:

http://agdproduction.com

Two forum threads are devoted to GaN-based Class D amp tech. See these URL links for further discussion:

https://forum.audiogon.com/discussions/gan-based-class-d-power-amps

https://forum.audiogon.com/discussions/which-class-d-amplifier-ps-audio-ghent-nord-merrill-or-other

Dowto1000

Here's a list of Pass amps with no feedback...
F1, F1J, F2, F2J, F4, M2, SIT1, SIT2, SIT3.

Those are all amps that will drive an actual speaker load. I'm not sure you could even call a .3 watt amplifier a "flea power" amp. Perhaps "microbe power" amp would be more accurate. I really don't think the ACA should be considered much of a measure of what characterizes Pass amps. That is an amp designed first and foremost to be VERY easy to build. "Professionally" building an amp designed to be put together by a 12 year old doesn't strike me as a monumental achievement. It doesn't sound like you know much about Pass amps. Go try a SIT, a J2, or maybe and F4. That F4 is designed for line level stages like you're working with to enable them to drive an actual speaker load.