I don't have any issue with headphones; I use 'em all the time. Yes, I've tinnitus, too, permanently, but I just keep the 'phones at a reasonable level. They're no different, as far as the ears are concerned, than listening without. I don't 'get' the 'tone' issue, either; if this is just for practising, it's just bass, isn't it (with maybe a backing track, or metronome...). When I'm practising, I'm not looking for 'tone'; it's so room/circumstance dependant as to not be relevant. Maybe that's just me (I'm a drummer...). I'd recommend 'closed' headphones, at a low level.