I know you currently only ("only"
support TCP. Flash now has UDP connection abilities via the RTMFP protocol. There is an interesting project on github (https://github.com/OpenRTMFP/Cumulus) which allows one to make UDP P2P connections without having to use Adobes FMS/Cirrus. I've been experimenting with it to allow for faster, twitch-type games, with some success. Anyway, it is an interesting project to watch. FMS is so expensive, and has so much unused functionality, if all you want is the P2P connections for game use. It might make for another interesting differentiator for Player.IO.
Peace
Jos