Single ended i prefer to the 701 to 6x0. my choice would be 701, 600, 650 in that order. 701 has the clarity, soundstage, imaging, and dynamics at this level.
Balanced w/ the right amp, the 6x0 are just better (and similar). The 701 doesnt scale like the 6x0 do. The 600 sounds similar to a 701 with just enough bass (minus the airiness...the perfect reference IMO). At this level, the 6x0 obviously surpass the 701 in soundstage and imaging. They just have so many more layers and better tonality. Playing Beethoven, this is VERY obvious.
the Atrios cant even compare at this level even out of the same amp, but for a ~150 iem that's expected. The M5 has a signature similar to a 650 but not as heavy and slow. IMO the M5 doesnt respond to any amplification after a certain point. I think it is destined to sound dark even using my brightest equipment. I wonder if a Aphex 204 can tune it?