Dude, I have both of them.
After getting my HD650, I would have to say Bose makes shyt ....not that shiit. lol. The crappy OE2 sound worths at most $30.
I'm pretty sure you would be blown away after getting your hd650. It is quite bassy and much detailed. Way better than OE2, even without an amp after your xonar.
Great to know you have both to compare. I know the senns are far better, but i have read they are picky with amps or sound a bit bass shy with the essence.
For the record, im more a speaker man but my current pair of speakers need to be a bit cranked up to sound good... with the neighbouring problem that has and when switching to the bose as you well know, arent up to the task.