Hello,
No current plans at HeadRoom to build amps with independent L/R volume controls. Back in the distant day, our original balanced-drive monster the HeadRoom BlockHead Balanced Amp did in fact have two volume pots that could be used in that application. Of course, that late 1990's/early 2000-era unit is long-discontinued and unavailable at HR.
However, for folks who are bit hard of hearing in one ear, a functional (if cheesy-sounding) work-around is the Sennheiser HZR62 device which allows any headphone to have separate L/R volume control:
Sennheiser HZR62 @ HeadRoom - Right Between Your Ears
Cheers,
Jorge
HR Sales/Product Manager