Headphone amps

No experience with those but I will give a thumbs up for the Cayin HA-6A if you don't mind a tube amp.

I would not buy anything these days without a 4.4mm pentacon balanced connection if you plan to keep it a while.

I have a Benchmark HPA4 and use it to power Kennerton Rognir Planar, RAAL SR-1b, and JM Audio Editions XTC-Closed phones.  I previously had a Quicksilver headphone amp but found it just a little too warm and bass-prominent with these phones so the BM is just right for me--fast, detailed, transparent, and spacious.  I tend to like that type of sound versus phones these days that are entirely too bass-prominent and dark.  Maybe that is because I grew up when phones and speakers didn't have the overhyped bass that are everywhere nowadays.  I posit that we have become conditioned to bass-heavy music.  The BM also has a line stage that can power other amps.

@shtr74sims, since you’re considering solid state amps in the $3K price range, I recommend also considering the Holo Bliss KTE. Check out the thread on Headfi on the Holo Bliss KTE. It’s more powerful than the other amps on your list but more importantly is its sound quality.

I own 6 amps that I can use to drive headphones including the Woo WA23, Auris Nirvana, Enleum 23R, Benchmark AHB2 (using banana plug to 4 pin XLR adapter), Holo Audio Serene KTE, and Holo Bliss KTE. The Bliss is my latest purchase and I think it represents one of best values in high end headphone amps in this price range. It’s quiet enough to drive high sensitivity headphones with no noise while being powerful enough to drive the hard to drive Susvara. Added benefits are that it’s an excellent preamp and it comes with a nice metal remote control.

Flyby alert — the OP has never responded and is MIA so consider you may be just wasting your time sharing your thoughts here.  

I cannot listen to solid state anything anymore. Has to be R2R DAC and tube amplification. Maybe I am used to that tone.

I have a few setups for headphones. The main system is Lumin U1 Mini with linear power supply, Denafrips Pontus II R2R DAC (latest firmware) going fully balanced into a Woo Audio WA22 tube amp to balanced cables on Focal Utopia, Meze Elite and a few other nice headphones.

A second system somewhat portable is a Raspberry Pi 4 with linear power supply into a Denafrips Aries 12th Anv R2R DAC single ended into a few different amps depending on the headphones....Icon Audio HP8 mkII (will run pretty much anything - surprised how good it is for under $800 used from TMR) also Feliks Euphoria for ZMF or other high impedance headphones, AmpsandSound Forge (runs about anything and will blow out your eardrums if turned up with kicking bass) and a Dragon Inspire IHA-1 (beautiful sounding but finicky about tubes and headphones - need to tube roll to match the particular headphone).

If you must buy solid state then Naim Uniti Atom HE is nice all in one (selling mine). Great tone but a little weak headphone amp for high impedance. Fine for most mid to low impedance headphones.