Q701 is a great headphone that even has some HD650 like qualities in the bass region. In fact, overall I'd rate the bass performance above the HD650's, but with the caveat that the overall bass presentation and quantity is better in the HD650's. Bass is more tuneful and well defined on the AKG's with surprising body and heft on some songs. The HD650's best them on many songs because the bass is like a lush cradle for the music. Personally I would rate the Q701's way above the HD650's on value for the dollar ($230 vs $499) and about on par in terms of absolute performance.
I've been finding that the Q701's are less amp dependent than some headphones and more source dependent. These things are really very resolving, and unforgiving of poor recordings especially in the treble region. They're less fun headphones, and more serious headphones. They can be a tad ruthless. On highly dynamic amplifiers I find they get fatiguing very fast and tend to be a little too hot in the treble region. On smoother more delicate sounding amps they sing.
They're a little bit of a conundrum because they're one of the cheaper high-end headphones out there but so resolving as to require a fair investment in your source, both recordings and equipment. But, it's a nice headphone and I think underrated.
