Any chance of getting a external bay with Networking?
Streaming movies over USB can be problematic for any router. Connecting a USB device to the router will require the use of Shareport as well.
Your best option would be to get an external bay with RJ45 network connections so the pipe is bigger and able to handle anything you throw at it. Also this would eliminate any router process that might be going on should others be working thru the router. I would also advise getting a external Gb network switch to help isolate the router from wired devices. I use a 24 pt and a 8pt with my host router. Stream movies from my server to my Boxee and can game and surf while all thats going on.