Please help me w/MKV streaming files stuttering while streaming WMC Win7 x64 Xbox 360

I installed a new PC at my place for serving up video files to the rest of the house via Xbox 360's as the front end devices. The PC is a Windows 7 x64, i5, 6gb RAM powered box that streams via Windows Media Center. I can see play most files but MKV files were not showing up which was to be expected. I downloaded and installed the new DiVX Plus Player for Win7 x64 as well as AC3Filter. Now all the files show up and while some play w/o issue many are VERY jumpy and constantly freeze/skip while trying to view. I try to pause thinking maybe it's a cache issue but even after being paused for several minutes it goes right back to herky jerky playback as soon as I hit play again. I makes them unwatchable. I was using TVersity before on a Vista machine and a XP machine and had decent luck with this and various codec packs but I really like the features you get from WMC on the Xbox versus what you get simply using TVersity on the Xbox so I'm hoping there's a way to make this work. I don't think my PC or my network would be the bottleneck as I'm hardwired and am running DD-WRT with the Flow Control enabled (I think.... Pretty sure that's a default setting on DD-WRT). I also don't feel like spending money for a new front-end solution since I have this at three locations (soon to be four) so it gets pretty expensive pretty quick to start changing out hardware.

Ideas?

I've been away for a while but I just streamed a movie that was choppy and I went to my PC that was serving up the file and the CPU was only at 1-2% and occasionally would spike at 9% but that appears to be way too low for what is being done. So is this my network or is it that the Xbox receiving it just can't handle it and therefore my PC isn't even breaking a sweat?? What is the best way to test this? Trying to avoid using TVersity again or converting each individual file due to ease of use. I really like the thumbnails and menus of WMC versus the plain Jane look to TVersity since it just uses the Xbox's basic vanilla menu system to search through files.