Is there something you don't like about your Ultrasones? I own the ultrasone pro 900 and love them. They have really good bass and have good detail. I haven't got a chance to listen to the 2900 but they are open and from what I here they the bass is more refined and the sound stage is expanded. The sennheiser hd650 came out in 2003, requires a headphone amp, and they have been discontinued. I haven't heard the hd650 but I do have the hd595 and they are very good headphones. My biggest problem with the hd 595's was the sound went out on the right side on two different pairs. I would probably say that the hd650s are going to be more analytical but i always found my ultrasones to be more fun and were my headphone of choice when I watched movies or played games. You didn't need to hook them up to a headphone amp to get good volume either. To bad the ultrasones weren't more comfortable and had larger cups. If you are wondering if you made the wrong decision and maybe could get better for the same amount of money, that is probably one of the biggest mistakes you just made a purchase with headphones. Graphs and reviews are only going to give you a less than general idea at best and but your opinion is what it rests on. I will tell you that I would have went with the ultrasones since they have detachable cables, low impedance, and I'm probably the only person on head-fi that liked s-logic. They are also less fatiguing. KG-Jag is right, you are going to have to listen to them to see if you like them better. If you are in doubt go to Best Buy, look for the bright red or black headphones that say "Beats" and listen to them about two minutes. I doubt you will be doubting the ultrasones after listening to those. Seriously though, how did you pick sennheiser hd 650 as a choice and didn't think about the Hifiman he-500(my favorite), hifman he-400(don't have......yet), or the akg k702(pretty good), or akg k550(awesome)? LOL there are so many headphones in that price range. Sorry about the grammar I haven't went to bed ye, but I hope this helps you out. Well good luck, and remember that there is no monogamy in headphones, just ones you haven't heard yet.