I have and can vouch for the Sennheiser. I doubt that they have that much more bass; they're just lower impedance (64 ohms) and thus very efficient--read louder. They have the greatest passive isolation of any phones I've ever encountered, about 32 dB, which makes them great for tracking and transcription. (Yup, I use studio headphones in my day job.) They have replaced my beyerdynamics (see below) in the studio. They were chosen on the basis of user comments on the Propellerhead Reason forums and the advice of the gurus at Atlanta Pro Audio. Specifically, they're very flat, just don't have the extended frequency response as those below.

For about twice the price I'd say go for the beyerdynamic DT 770 Pro. I just retired my 16-year-old pair from studio service, but I still use them eight hours a day on the job. Accurate, comfortable, durable, and with about 21 dB of isolation. Not as efficient as the 280s, but tremendous power-handling capacity, which again translates as loud if you've got the gear to drive them.

HTH,

Richard

"My primary musical instrument is the personal computer."