Ok so I managed to pinch the M9 off my wife for a mo and just did further listening with the M6 and M9 and BTR3 and even threw in the Mojo and the V30 phone into the mix; with the FH5's there's just so little in it between all 4 devices in fact, it's really a case of trying to remember nuances between player and wondering if I imagined them. With the Beyerdynamic T1 (600ohm) there's definitely more clout with the M9, it needs around 95/120 on the volume as opposed to around 110/120 on the M6, but these are 600ohm beasts we're talking. And there's more "presence" with the M9+T1, than the M6+T1. Interestingly the V30 drives the T1's really well, better than the M9 imho, I guess the hi-ohm switching kicks in nicely with them and the amping gets ramped up accordingly.
So... my initial comments in the other post apply. I'd still probably go for the M6 or get both M6 lol, if they were the same price. It's a sheer delight handling the M6. The M9 is jarringly angular and relatively bulky for the same screen size and res.. Love the M6.