The AKGs are amazing and great values... You can have headphones a little more technically proficient when you buy Summit-Fi headphones, but even with my STAX I still find that I really enjoy listening to my K612 too.
According to reports, the original Annie pads were less deep and if the KXX are using those then they're probably about as deep as the K612 pads (though memory foam), while K712 pads are juuuust a little bit deeper, like hard-to-see-how-much deeper. On many-hour gaming sessions, sometimes I miss the featherweight AD700, it was easier for me to forget the partially on-ear pads of the AD700 (meant to push/angle your ears against your head) than the slight weight increase of the AKGs (235g or 238g is still really light!), but both were great for me and five hours of gaming... This includes the K612.
If you have a Mixamp already and want more power, you won't find a substantially better DAC that processes virtual surround until you get the X7 which is definitely a higher-grade component than fits in a $100 budget. A few inexpensive options for just an AMP that you can plug into the Mixamp (and thus use the chat balance feature) would be a FiiO E11k or a Fred_Fred_2004 3-channels amp (custom built in an Altoids tin, with a 9v battery, reviewed in head-Fi member ClieOS portable amp roundup). Of the entry-level DACs that process surround sound (wish we could call them gamer DACs, calling them "Mixamps" is like Kleenex, using one brand that's not the best to name an entire product segment), I haven't heard Tritton's processor but all the other gamer DACs sound a little better than a Mixamp... I choose to get by without external chat balance mixing.