I love the m8 with my hd 650. W/o the hugo i would've been contented with the m8 (it made the CLAS -db & RxMk3B+ moot for me). But once i got the hugo and it paired well with all my iem's, the m8 has been secondary. I'd like to stress that the m8 paired well with the hd650. But i sorta didn't like the hd650 & hugo combo.... Yet.
For me, everything comes down to the pairing.
In general terms i found the hugo more musical/analog than the m8 w/c sounded more neutral/clinical. For my hd650 its a no brainer, i'll use the m8. For my ie800 & jvc fx200 i can use both but prefer the hugo.
Lastly, in a 2 min listening session, i had the chance to demo the q701 in balanced mode with the m8. I couldn't stand it as the highs were piercing my ears.
I hope this helps.
Great! Sounds like I just need to get a M8.