Grab a copy of MPC-HC -- it works for most every container & format. Even if you don't like it for a front-end it's an excellent tool! I consider it my baseline whenever I'm playing with my system 'cause I never get any CPU usage lower than when I'm running MPC-HC for playback. BTW, .264 playback is a BREEZE with my E-350, it's HD MPEG2 playback that's the difficult format - apparently it's not fully supported by the HD6310.
I'd say it's a Z thing, more specifically, a limitation of whoever they're using for their BIOS -- have you checked for an update on their site?