audvid,

If you plan to purchase HD600, you might want to invest on some good quality headphone amp to go with it later whether it's home use or portable. When I auditioned both HD580 and HD600, I preferred HD580 for non-headphone amp setup while HD600 really shined with the quality headphone amp. Now Sennheiser's top model headphone is HD650 which I didn't have a chance to listen to it yet. Here is another website for all headphone discussions, www.headwize.com; they have all kinds of reviews, info, suggestions for diy, etc.