Is the O2 (Objective2) connected to your computer or the FiiO E10K?
I am using the e10k as a dac and the o2 as an amp. seems to be an improvement in terms of flat response, the e10k was either a bit too bassy or lacking bass depending on whether I put the boost on or not. the pairing seems to be working ok and I think this should work well for me. certainly get's loud enough. I don't have the 770's yet but I imagine it won't have any issues and the bass response should be a bit more natural.