The OTL work best with high ohm headsets usually like a Sennheiser HD600 which is 300 ohms or the Beyerdynamic DT150 600ohm (great cheap headphones but terrible horrible excruciating comfort and not so great dynamics) -
I asked Valentin a year ago about making an adapter for the low imediance Kennerton headphones to step up to 300+ ohms so they would work with OTL and he is still working on the idea- they may be toying with it soon again... I do know they are working on a killer crazy cable that is modular in nature...
anyway...
The gh50jm edition benefits from clean class a power like a Benchmark hpa4 or Ray Samuels Apcache or if those are too high in price as they certainly are - maybe
this for $509 Singxer S
A1 which is cheap!
I don’t know if the low 33ohms needs or benefits from otl design- when I tried my Bottlhead Crack SB it matched perfectly with HD600 and did not at all for any Kennerton.
I know a few users do use tubes but I never found one that I thought would match well or better than class a SS except I do know the all-tube design, Class-A, transformer-coupled, single-ended triode (SET) amplifier will work but never tried sadly. NO go on any OTL as far as I understand unless Kennerton steps up Ohms to 300 or 600 with adapter...