Playback issue with media center + 360

I have a simple network built out of the following:

1 Windows 7 Ultimate x64 Media Center
2 Xbox 360s
1 Synology DiskStation NAS

Everything is connected to a gigabit switch over cat5e. Obviously, the connections to the XBoxes are not gigabit, but the connection between Media Center and NAS is.

My issue is this. I have all my media stored on the NAS, and I can watch it just fine using my Media Center when I view it directly through the Media Center (connected to my plasma tv). The trouble is that when I try to access movies using either of the Xboxes as media center extenders... the movies won't play. The files are m4v.

Is this network related? Obviously, Media Center can play m4v as I can do it right on the server.

Thank you!

So a registry hack would fix it? That post is a little dated... does the "hack" still work in win7?