I've been burning up the wire, searching for the solution to your problem (I noticed it in Tilted Gaming) and haven't found anybody with your particular problem.
I would say....
First, I would double check the firmware. I know, I know, you're not an idiot, but I've done some pretty stupid things and overlooked some pretty simple answers before. Sometimes it happens.
You mentioned it's a befsr41.
I assume it's running the 1.04.8 or 1.05.00 version of the firmware.
Second, since the IP addy of the X-box is static, I would use the router to set it up in a DMZ. Your X-box is probably pretty safe being "exposed"
I found an ftp link to the manual in case you lost yours or don't want to fool around with it willy-nilly. Not your specific manual, but it covers several similar versions. You can find it
here.
I've read about problems related to port forwarding. Turn it off. Microsoft says
you don't need it.
You could try running the x-box through your computer using ICS. I don't know if that would affect lag much, but it's worth a shot. You would be using your PC as a big ol' router. If this worked and you could see everything, then it would mean the original router was the problem, right?
Does anybody else run their x-box through a router at your dormitory? If it's just you suffering through it that's one thing, but if everybody else has the same problem than that would exonerate the router, no?
I don't know if this will help, but what the hell, eh?