High end high quality int. amp for low level listening

I think you need to back up and ask more fundamental questions.  First, is there any evidence of the amp reaching clipping (or coming near)?  if no, and if you are listening at -60 dB i doubt it, there ought to be little if no benefit.  heck, get a multi meter, get an average rms value and assume a peak:average ratio of 10.
Second point, think about the system balance My opinion is that the Sonos Fabers can be bright and a bit harsh. Tubes, or tubey solid sate will help that.  You may be giving up a lot to speculate on a possible, but unlikely, benefit.
You mention a bigger power supply.  Back to that 10:1 i mentioned above - most amps clip due to voltage limits, not current limits since the capacitors in the power supply can deliver power for momentary creschendos. Caveat: if you play mostly compressed "head banger" rock this is not really true.
Move slowly and do your homework.  You'll et too many suggestions on how to spend your money rather than whether you ought to in the first place, IMNSHO.

G(the guy trying to finish his integrated amp design LOL)

I suspect, IF you had more power you would listen at higher levels, a little louder, some times, if not frequently. Probably now wanting to push your existing amp to the limit now.

I also agree with Eric, at low levels, a bass boost would make a more involving musical experience. ’Loudness’ circuits when used as intended, automatically and progressively boost bass as volume lowers, to compensate for our hearing system’s properties, reducing and eliminating the boost as you raise the volume. Few modern preamps include 'Loudness'.

https://en.wikipedia.org/wiki/Equal-loudness_contour

Of course, you could keep the amp and change to more efficient speakers instead.

Existing amp: do you have another space where you could set it up with more efficient speakers rather than sell it?

Something like that makes more sense. Those recommendations for a more sensitive speaker or a higher powered amp still have me scratchin’ my head!

Yeah…
And I’d be interested in what DACs you’re choosIng from.

celestial__sound,

If you do get the Hegel H390, you get a pretty darn good DAC build in.

All the best.

JD

Hi Celestial Sound.

Those are all wonderful amplifier choices you are proposing, and your current amplifier is really a beauty too. If I understand correctly, you are happy with the sound yet feel there is more the speakers can do? 
Like yourself, I have stand-mount mini-monitors - the Evolution Acoustics Micro One. With respect to specifications; impedance is rated as 6ohm (+/- 2ohm impedance variation) and 86db sensitivity. Frequency response is stated to be 30hz - 30khz, although at 30hz I don’t think there is an aweful lot of energy. They do sound full-bodied though, and are superb. Its hard to believe these little stand-mounts can produce sound the way they do. A testament to top level engineering.
With my Micro One, the volume knob must be ‘goosed’ more to get the db and energy I want from them, although I don’t usually listen at loud levels either.  So you are right in contemplating the possibility of a better match. You will probably find, as I have, that a more powerful amplifier will generate better sound. 
Given your generous budget, I would consider Parasound as a contender too. Of the amps you have listed, the Levinson 5805 might be my choice. It’s a daunting proposition without an audition, so that’s really key. Are there dealers for those specific brands within driving distance for you? As they are stand mounts, you could always (very carefully) schlepp your SFs to the dealer. I am sure they would have stands you could use?
Best of luck in your search.