Here is some info about some Ultrasone line differences. LazBro 123 replied to me in a different thread and thought I would quote him on this thread, as it gave me some answers. He starts off by informing me about his experience with PRO 900.
LazBro 123 quote:
"I have used my 900 for gaming. It's really good for that purpose. Great imaging. Great soundstage, sounds pretty open to me. Your sound card will drive them fine. I got a nice HifiMan EF2A Tube Amp/DAC for my PRO 900, and they really, really benefit from it. Sound is much warmer, and the bass is even tighter, deeper and gains impact, mids are brought out a bit, and the highs are smoother. They even sound fine straight out of a computer or out of an iPod, it's just you're not getting their full potential. If you're a basshead (like me), the PRO 900 are definitely worth the money. I also have an HFI 580, and the PRO 900 is a HUGE step up. The 580 sounds tinny in comparison, less bass and not as defined, harsh upper mids (lower mids are their strong point), and unbearable highs. Less detail as well, and sounds artificial (colored). The DJ1 is an HFI 580 (A bit louder because of the 101 db vs 104 db sensitivity, but the exact same headphone), and the DJ1 PRO is a PRO 550 (Exact same headphone, no technical differences). If you can get the PRO 900, don't even think about the HFI or DJ models.
Just to clarify, the PRO 900 has the most bass I have ever heard in a closed headphone, without bleeding into the other frequencies. and still retaining a great amount of detail overall."
END QUOTE______________________________
Thread Link: http://www.head-fi.org/t/599421/ultrasone-hfi-580-vs-ultrasone-hfi-780-vs-ultrasone-pro-550-vs-ultrasone-hfi-2400/30#post_9316628