IMHO yes.
To cut a short story long...I bought my wife the M9 for xmas, and in return she got the me M0 which i thought was fine as I'm spoiled for musical gadgetry (I have the X7ii and other kit so I thought the M0 would be fine to fill the ultraportable hole, lol). Then I became distinctly jealous of my wife, haha. Well... jealous is a bit OTT, but the old gadget lust kicked in when I got my mitts on the M9. So I was actually about to try and sneak the M9 under the radar then noticed the M6. Whoa! I was smitten. Couldn't find it in stock anywhere (this was mid jan i guess?) and was going back to consider the M9 again. Managed to find the M6 in stock at B&H and pulled the trigger. 2 days later i was comparing to the M9.
Honesty... if the M9 was the same price I'd probably go for it, MAYBE - the decision would be harder, but it's not.
I run balanced on the FH5's (works with my X7ii) and I'd maybe have gone for the M9 (if same price or not much in it), but even then the form factor is really great on the M6, it's just nicer, imo, than the M9. which is bulkier, heavier and "sharper" than the M6. The M6 is like a smooth pebble in comparison and so small and light. Bang for buck, it's a no brainer. 2 for the price of 1, lol. I'd get 2, m6's in preference to one m9 any day.
Ill try and run some further listening tests in the next day or 2, will try also with my big T1 cans to compare output, and maybe the T1's will resolve more too from the M9.