Sorry, this is a long and confusing issue! About a week ago, without any change to my network settings, I began having a problem with streaming 1080p content from my media server to a router, wired to a switch that serves a few devices in my home theater (including a HTPC, my Boxee Box). Every 15 seconds movies have to buffer. After a while, I narrowed it down to the switch, since wiring the Boxee Box straight to the router caused the movies to run perfectly.
Logically, I thought the switch was the problem, since I really made no changes on my network/DD-WRTRouter other than running a Minecraft server (which shutting that down made no difference in network performance). I ordered a brand new gigabit switch, same problem. Pinging the BoxeeBox returns 0 packet loss whether it's connected to the switch or router, but movies still play perfectly fine when directly connected to the router. Different cables didn't help.
Ok, well, I thought maybe the other devices on that switch were causing some sort of conflict.. changed the BoxeeBox's static IP just in-case, unplugged every other device from the switch so that only the BoxeeBox and Router were connected to the switch. It worked fine! Yay! Tried a different cable, still worked fine. Great, I thought, so the problem was never my switch... plugged the old switch back in, then the problem returned. Ugh. Changed back to my new switch (each time power cycling all of the network devices) and the problem persisted, even with the SAME EXACT setup I just had a few minutes previously that worked fine. Tearing my hair out at this point.
Since that moment I still haven't been able to reproduce a perfect stream unless the BoxeeBox is directly connected to the router. This doesn't make ANY sense as I had this setup running perfectly fine since November 2010. I am COMPLETELY out of ideas other than running multiple ethernet wires to that drop or running all the other devices on wireless. I appreciate any help, thank you!!