As an owner of the 5210mk3, I would recommend the non stepped controller for low sensitivity phones(unless, is it 64 steps? then maybe). On low gain on the mk3, I typically listen at about volume 2-3 with standard dac output(~2v) on the HE-500, so I imagine with the TH series the volume knob would be particularly sensitive and you might find yourself wanting to be in between steps which might not be a problem depending on what your opinion on digital volume control is, probably depends on how your dac responds to such.
I previously paired the bakoon with the MHDT Labs tube output HAVANA dac for a more natural sound and really by that I mean non-fatiguing. I did however have to do a bit of tube rolling to get the sound right, I was using a sharper sounding tube to pair with my taboo amplifier. Once I switched to a tube with a bit of warmth, I felt that this was the right balance between high detail and non fatiguing, natural sound. A dac with a more analogue type sound would be more in line with what I would recommend for those considering. I assume this applies to most phones as I never found the HE-500 to be fatiguing in any setup until this one.
As for output, the only time I found myself using voltage was for IEMs however, I never tried any higher impedence headphones(>100ohm), so that may change with impedence. The current out is a feature that makes the bakoon unique, so that's probably going to sound the best with most phones. This is a highly detailed amplifier that does not miss a thing. It's what I would imagine when thinking of TOTL solid state. I would still at some point like to try out the HE-6 as well as TH-900 with this beast amp.. anyone want to loan me?
I can probably answer a decent amount of questions pertaining to the amp. I know it well so ask away.
HDA-5210mk3 has a great bass impact, super spacious soundstage and with a good depth, some grain in the sound, but the best resolution out of all the amps here.
What is meant by "some grain in the sound"? Background noise?
I imagine by grain he means not to the absolute fullest resolution. However grain is something I never particularly noticed. I think depending on the dac, the bakoon can fully show the apparent weakness of said DAC, for example sometimes I felt that the sabre chip was sounding a little too digital sounding compared to the tube output+burr brown of the havana. I never noticed any particular grain coming from the bakoon alone, but that might be something that becomes more apparent with lower sensitivity phones for all I know.
The other phone I used heavily was the t50RP paradox headphone which to me, the sound was like something you would use for mixing or mastering. I wouldn't call it particularly interesting but I definitely heard everything. It just wasn't musical enough for me, which is in my opinion, the signature of that particular phone.