Darn, I almost had the perfect headphone for you to try out before you mentioned that you DON'T want closed headphones.
Before I saw this post I was doing A/B testing between my Grado SR-80 and Koss Pro DJ 100. I can't believe how similar each of them are. It's almost like it's the big brother of the SR-80. It has more bass, slightly better mids and more tame highs. Way less fatiguing. The Grado SR-80 are really growing on me, but it only took about 3 years! Soundstage is also pretty impressive for the Koss headphone being closed. Instrument separation reminds me of the DT-880 more then any other headphone. Unfortunately they need an amp to sound really good and to bring out the bass.
I also don't like the DT-880, but I only tried the 32ohm version and maybe that's why.
I can't think of anything else that would work, but your description is also exactly what I look for in a headphone. I do like a lot of bass, but not too much. The only problem I have with the SR-80 is there isn't quite enough bass and the highs can be annoying at times with certain music.
Hopefully you can get a few other suggestions. Right now my favorite headphone for the best mids is the HD-600, SRH-840 and Pro DJ 100. Can't afford the ESW10, even if I could find them. They sound interesting though.
EDIT: HD-650 might be good, but I'd suggest trying out the HD-600 first. I actually disliked the HD-650, but some people prefer them. The highs are just about perfect on the HD-600. Just about a step below where they would get annoying. The bass is more then enough for me. I just wish they were a bit easier to drive. My Total Airhead is constantly yelling at me when I try to use them with it, so I have to instead use a receiver, which powers them perfectly fine.
Edited by tdockweiler - 9/19/10 at 7:32pm