hi there,
sorry, but that's the big drawback of using usb for high-bandwith devices. usb can't push enough data to the farther devices fast enough to keep up with their needs. when attached through a hub, each data packet has to include information about which port on which hub the data needs to go. that eats into the bandwith slightly as does the longer total distance the data has to travel. the real kicker, though, is the time the hardware in the hub spends routing the signal. add it all up, and your data doesn't make it to the burner or the a/v box, which rely on data being there _exactly_when needed, quite fast enough.
hope that clears things up,
ster