I just got my pair today, I've been using ultrasone hfi-780s for a while, only source right now is my musiland monitor 02 which I don't think is sufficient enough for the 650s because my 780s sound louder/better. The only amp I have is my portable Alo rx which again the 780s sound louder/better, with the rx i have all the volumes up on the 650s and its not phazing it so I'm gonna have to invest in an amp it seems like
How many hours of burn in to these cans need?
I have a pair of ALO-780s, and they do not compare favorably to my HD650s. ALO/HFI-780s have very aggressive and overpowering mids, IMO, which makes them sound very involving and 'fun,' but you also lose a lot of detail and space (and really anything that isn't in the mids) My HD650s on the other hand, have a much more balanced and open sound, but they certainly aren't the most aggressive headphones ever made, so you're most likely missing the really forward sound that you get from the 780s. Try listening to your HD650s exclusively for a week or so to get used to the sound, and then switch back. I'm sure that you'll be amazed at how much more detailed, neutral and expansive the Senns are then the Ultrasones.
I wouldn't recommend any dedicated burn-in, there's no point because it won't help you get used to the sound signature. It will only waste the batteries in your amp. I'm a proponent of 'burning in' on your head, because I feel that there isn't any appreciable mechanical burn-in, only psychological adjustment.
As far as an amplifier, I definitely recommend going for a desktop amplifier in the near future, but make sure that you do lots of research so you know what you'll be getting into. Don't rush into it, your HD650s will still sound pretty decent out of your current setup.