Welcome to head-fi. Sorry about your wallet.
I will probably use my M8 to drive my HD580s, along with Fostex T50RPs with Alpha Pads. Both need some amp power to sing. I am curious about the balanced vs. unbalanced question too. Convenience is a big factor for me, but I would be willing to do some mods or cable replacements if I can get some sonic benefit for it, and on these two headphones in particular since they are so hard to drive.