I know this is not really convenient but have you tried Play To with M2TS files? (They work for me on 360). Most common MKVs have H.264+AC3 in them which is same as M2TS. All PS* and Xbox* support that format.
DNLA - streamed a few avi and mp4 movies with no issues using the Play To function on my laptop. As expected, mkv files did not..
Try remuxing a MKV into M2TS and see if that works.