...you have got to be fuggin' kidding me. Now, I don't mean to traduce those Senn fans who have posted before me, but *come on*! Sennheiser HD600s for "punk rock, trance, techno, electronica, a little pop"?!?!?
Surely, you're all kidding...
Let me tell you from personal experience, zbuddah: you will not enjoy that kind of music through those headphones. Based on the nature of the music, I'd guess that you are looking for a "I feel like I'm in the club slamming" kind of intimate sound and the Sennheisers are not going to give you that as well as Grados will. Not by a long shot.
I have not heard Beyers or some of the others, so I won't comment, but let me tell you: for the exact kind of music you like, the Grados are *by far* going to give you the most enjoyment. Synth lines are incredible and will take you over...you will hear "those little details" and much more. They're efficient and merely a JMT amp will do you damn good.
I've owned and, naturally, extensively listened to Grados (SR-80s, SR-125s, SR-225s, RS-1s), Sennheiser HD600s, Ety 4S's, Audio Technica ATH-W100s
I maintain that Sennheisers are mf'ing excellent for accurate reproduction of Western Art Music, but when any of the styles you mentioned enter the equation, they relatively just **** the bed.
I would at least recommend getting a trial. Buy them from Headphone.com. Order a pair of Grados and a pair of Senns (and maybe some other ones people recommend here), listen through your rig and send the one(s) you don't like back. You'll have your refund before your credit card statement comes and, most importantly, you'll be happy, not wondering "could I have done better"?
Believe me, save yourself the headachey, wallet-thinning practice of buying and selling in search of what you want. It super-sucks.
I really hope this helps.
- Matt