Any ideas?

No, but it's interesting that it works for you with Rio Audio Manager. I've got almost exactly the same setup -- BEFW11S4 and WET11, only with Empeg's (unreleased) unix receiver server daemon based on the Rio Central code -- and I get dropouts in songs encoded at more than about 200kbits/s. I haven't figured out what's going on yet -- there should be plenty enough bandwidth. I'll try it with Rio Audio Manager, and then I'll try it with a packet sniffer...

Peter