MTS files play fine over the network; I used a test file from a Panasonic camcorder.
Also success with Xvid, DivX, DivX HD, wmv, wmv HD, vob, and various transport stream.
I had no luck with MKV (which isn't something Humax has claimed to support either), but some people have reported more success; MKV is just a wrapper, and it really depends what's inside it. It's such a broad church that it's probably safer for Humax to say "not supported" than to say it is, and then have complaints when certain files don't play.