... And in addition I want to buy some AKGs in the future. I read on MLE guide about Fiio E09k and Fiio E12 and want to know, which of these will be working better with MA900 and with potential AKG in the future. Or if you think that there will be better choice, tell me about it please.
Thank you for any advices.
Technically, the E12 has lower output impedance (doesn't matter with the MA900, not really with the open AKG's either) and lower Total Harmonic Distortion (THD) than the E09k, and the E12 has that subtle bass-boost switch, but really your choice ought to be based on "do I want a desktop amp or a battery-powered portable?"
In short, devices like the Mixamp translate a 5.1 surround signal to a stereo headphone mix, with a headphone jack for ANY headphone to plug into.
The Xonar soundcard on the way to you can also process surround from your PC games into a Dolby headphone mix.
The Logitech headsets you mentioned earlier have poor audio quality for the price, and yes you often can have your budget benefit you more by buying a good stereo headphone and separately a cheap lapel mic (the kind that clip onto a shirt collar). Pretty much any headphone mentioned in Mad's guide would be a good choice; pick one that fits your budget.
I said "may" be a better value. The bumps don't bother everybody, and replacing the headband with AKG's flat one is hardly the only option. The pads themselves aren't much different for comfort, just some people might prefer the looser bass, so for someone on a budget new pads are optional. Also, sales come and go, you can't state the lowest sale price you've seen as the average street price, the Annie's are likely to go up.
So there are reasons to spring for the K712 (or Annie's), but for many people, being able to easily snag a pair of Q701 for $220-$250 + $5 seatbelt wrap (or just cutting off the bumps with a razor) is an entirely viable option that will give them great value.
When I actually write a K712 review, I'll be sure to mention what you gain over the Q701, and leave it up to the reader to decide if they value the differences enough to pay the price difference.