almost anything can be built in a dual-mono configuration. the odd exceptions are some tube amps whose designs "share" a "double triode" tube for gain. the morgan jones (earmax) for example can only sort of be built dual mono with 3 tubes.
the only thing holding most builders back from a fully-dual-mono design is the fact that you need 2 power supplies.
2 transformers, double the caps, double active "bits," double the inductors... double the price...
it is not too hard to make a dual mono m^3. the 22b should be about 10020% better & easier to make dual mono to boot.
the dynhali (the one with the BIG output transistors) is a mono board. just buy 2 power supplies...
are your headphones terminated in a 4-connector plug?