I've got a Denon AVR-5803 controling 3 Zones. 2 Pioneer PDP-M502MX Plasma TV's, and the Sony CX777ES DVD changer all hooked to a RocketPort Serial HUB.
The Serial HUB connects to ethernet, and the serial ports map a PC on my local network with the comtrol driver installed. The just show up as COM3-COM10.
The Denon 5803, and the Plasma TV are controled via MLRS232Send commands right now. The Denon has a great easy to use protocol that's all ascii. There protocol supports two-way communication for getting current mode, volume, tuner freq/preset, etc from the 5803.
I'm working on a dedicated Plug-in for MLServer that will enable the two-way commincations with the Denon when Mainlobby support is added.
The Pioneer Plasma is also being controled via the MLRS232Send plugin. It is a hexidecimal protocol, and is a little more difficult to get going.
If anyone needs sample commands for these devices, let me know.
The Sony CX777ES protocol has to have a checksum on each packet, so a MLServer plugin is required for anything interesting. I have written MLServer plugin for the CX777ES that seems to work well. It does not support any of the two-way functions of the DVD player yet. If anyone else is interested in testing it, please let me know.