A good start, and one which pretty much rules out OTL models.
Cayin N8, N8ii, C9 (nice, but fussy about charging) and N30LE. The first, and the last (in “Classic” mode), have the most tube/SET flavor.
There’s the A&K SP2000T (wouldn’t buy; slow and runs some ancient land-before-time-forgot version of closed Android).
A bunch of DIY options from Pete Millett; I’ve built several and they were all very enjoyable.
I think iBasso did a DAP that had an optional NuTube amp module …
There are probably others, just not coming to mind.
It’s a lovely sounding amplifier. Distinctly flavored, and nicely tubey.
It’s a fair bit bigger than it seems. Battery life is very short. The charger is not USB so you have to keep that with you, also. And you need to be careful with balanced input (use Woo’s cable or don’t do it at all).
I quite like the various Fireflies models … though am less keen on the DACs.
WA-6SE is very nice. The WA-6 is too, but the SE is a better bet overall.
But these are all a far cry from their WA-5 (VERY tube dependent), WA23 and so on.
There are various other options. None sound like good 300Bs … and even then the 300Bs you use a significant factor. Also, steer clear of “fully balanced” tube amplifiers if you want the most tube flavors … as balanced designs will cancel out the even-order harmonics (which defeats the point).
Which leaves, mostly, hybrids. The current Schiit Vali is a nice option, at low cost. Might give you an idea of what you’re getting into. Lyr+ is better still. But neither is “very” tube-like. Valhalla is (or was) more so … and is one of the few OTLs that might work well with low-impedance planar cans.
The Pro iCan is probably my favorite, reasonable, hybrid. It’s really a do-it-all option. And it’ll drive almost anything.
Unfortunately, good tube options are expensive (good iron costs, so do good passives). And then most of them need good tubes, which are more expensive still.
The DNA amplifiers tend to be better than most when using non-optimal tubes, but you’re looking at a Starlett or a Sonnet 22, I think, around $2K.
…
Not sure how much that helps …