I have a 2005 Lexi 255GTS and the setup should be similar to yours. I don't have a schematic for the TV/sound system but you might contact:
ConcerTone at (574) 534-3167 for a "Systems Connections" manual. The ConcerTone controls the inputs to the CD, the DVD and the TV. They might be able to provide a wiring schematic as well.
Also, if the previous owner removed the satellite system (and the antenna), mine is a KingDome Satellite System and their phone # is (800) 982-9920. Ask for a "Installation and Operating Instruction Manual" and a wiring schematic.
Good Luck and I hope you enjoy the 255.