Choppy MKV playback on ATV1

So I’m loving my ATV1 again since installing aTV Flash. Streaming via XBMC/Navi-x is great. So is saving my DVDs to my external HD and playing them — DVD menus include.

My biggest annoyance is that I am unable to play MKV files. They’ll play actually but they stutter and stick so badly that I end up having to run them on my Roku. I can understand this happening with 1080p MKV files. I also encounter the issue with 720p MKV files. Is there a trick to getting these files to play smoothly on ATV 1? Is there a tutorial that I overlooked here? Any advice would be appreciated.