Bass and mids are pretty much a seesaw in almost any headphone. More of one means less of the other. That said, if the headphone is clear and detailed, the mids are still very audible and musical in bassy headphones. The HD-600 is pretty even balanced between mid-bass and mids, but it starts rolling off for sub-bass, which is important for hip-hop. Thus, I don't recommend it for that that purpose. The HD-650, if you can stretch your budget, has better extension while retaining the mids, so it might be a viable option. Both of those are hungry cans and need some amplification to sound more to their potential. The Pro 900 has lots of sub-bass, and even more mid-bass. This seeps into the mids a little bit and recesses them, but I personally don't find it a huge deal. Others do, and you might. The Denon D2000 and D5000 are kind of a middle ground between the HD-650 and Pro 900 and are certainly worthy of consideration. The Pro 900 and the Denons are fairly easy to drive for higher end headphones, and don't need as powerful of amplification as the Sennheiers, though at least some is recommended to more fully realize their potential.
Edited by LithoJazoSphere - 1/17/12 at 6:01pm