I've only had the Q701, but I can give some basic comments on it.
What it does well: Large, wide soundstage, natural midrange, detail extraction
What it does poorly: Bass impact (though extension is good), too bright for some tastes
Suitable Genres (no order): Acoustic, folk, or indie rock, classical, world, vocal, ambient
Unsuitable Genres (no order): Rap, bass-heavy electronic, metal
It requires an amp, but not necessarily an expensive one. Don't buy it if you don't want to get an amp. I used a JDS Labs Cmoy with it, as well as a Little Dot MK3.