I've had both the Zoros and the M80s, and ended up selling the latter. The m80s have a very forward midrange and a sort of "in your face" sound, while the Zoros have a surprisingly neutral signature with decent bass and good mids. They do have a weird roll off in the treble that makes certain instruments sound a little muffled. Build quality on the Zoros is decent, but the M80s feel much sturdier.
The main reason I kept the Zoros and sold the M80s is that the latter were so uncomfortable that I couldn't stand keeping them on for more than 30 minutes at a time, and I have a fairly average-sized head. The Zoros are relatively comfortable, on the other hand, and the fit is much better as well.
Bottom line: the M80s are fantastic headphones, and definitely better than the Zoros in terms of sound quality. Having said that, they cost at least twice as much, and the comfort issues are a real bummer. I'd recommend getting then Zoros while Woot still has them for $45($55 for the HDs, which I haven't heard) because at that price the level of sound qualify you're getting is phenomenal.