i have my fx tube dac still... after reading the stuff about the shootout in arizona -- bought it stock sounded very musical but somewhat rolled off and veiled with good tubes in it (stock chinese tubes turn up the treble some, but a little grainy) then sent to chris j/wally to upgrade level 2 mod - comes back cleaner more transparent more extended - sounds right with proper, good old stock ax7’s in it but the treble can still be a lil problematic (sibilant) now that caps and wiring have delivered excellent extension - maybe the thing needs a thousand hours of break in lol...
sibilance not as bad as dena ares2 or bifrost mb, but still there on some material - tried various cabling...
so overall i like the mhdt and audio mirror (with tube upgrades) more, or the lovely older mf trivista or ava fet topp dacs more than the fx for ease musicality and insight without force feeding treble detail -- but i haven’t thrown in the towel yet on the fx
i am not a headphone guy so can’t comment on how good the hp output is... but that lil volume control is not the greatest... imo best to leave it on full blast for most clarity and control volume elsewhere