I'm listening to my K701s right now and I'm more than happy with the sound. It's bass-lite, because of the open-air design. These are headphones that pick up the upper register well but let the bass spill out. To fix that, you simply use a decent amp, one that will boost the bass you've lost. In the world of sound, bass is a lot less of an issue than muddy mids and highs. Get the clarity first, then worry about the bass. The K701 is an exceptional headphone, if you know what to do with them. Both Grado and Sennheiser have imitated the AKG design in their upper-end models. Because of its doped drivers and more euphonic shells, the Grado GS-1000 and PS-1000 will give you more bass (as will the Sennheiser HD650) but you can get that bass with a decent amp.
I'd rather buy a K701 for a few hundred dollars used, and then add a decent amp for $500, then spend nearly two grand on the "best" from Grado and Sennheiser. In fact, I already have.