007, I strongly implore you to go to www.headfi.org. The people there will tell you EXACTLY what you need. I LOVE it there. It's an absolute gold mine of info on headphones. Just a word of caution: their motto is "sorry about your wallet", so keep an eye on the credit card
As for me, I have an HD-590 and I love it. It is not as loved over there, but they are true headphone nuts. If you do decide on getting either an HD-580, HD-600, or HD-650, they REQUIRE an amp. A really good starter amp is called a Gilmore Lite. Unamped Senns, I would recommend either the HD-590 or new HD-595. The 595 is a little hard to get due to a factory fire at Senn but they are just now coming back in stock. Some things to think about. Definitely go over to headfi.org and run it past them though; you will be blown away at all the choices