Dan (MrSpeakers) also posts here on HF and there's a long thread about 'em if you wanna look into them. I haven't heard 'em myself but impressions look pretty good, not sure if they'd be up there w/the DT 770 in terms of sound stage tho. The pads look superb if you're not opposed to leather (it's real lambskin leather).
There's varying degrees of open headphones, sort of, some just seem to leak out a lot more than others... But most are gonna leak out enough that anyone in the room will hear it unless there's also music playing over speakers or something (in which case you'll clearly hear that). So yeah, not recommended if you routinely game in the presence of others... Unless you have a closed option as a backup to switch to, it's gonna bug either you or them.
I think you have a good sense of what MLE means by fun factor, tho ultimately the exact balance is gonna be subjective and something that's particular to your personal taste... Some might crave a lil more bass impact, others just want it present and detailed, etc. I've never heard the 350 but if it's anything like the 360 then it's kind of at the opposite end of the spectrum as the M-100, but I think there's plenty of room between those two (as far as where other headphones would fall).
Mixamp will struggle w/some $300-range headphones (MD possibly) but not all, AT A-series are easy to drive (as are the two you've tried), DT 770 80-ohm version might be fine too.
Edited by Impulse - 3/9/13 at 9:54am