Hey Mike, glad to help. This board is an incredible source of information. Much of my current knowledge of car/boat audio has come from here. If you want to see some really sick installs check out Grant and Clays work at
http://www.soundillusionsaudio.com Some day I aspire to be that good.
My boat originally had the old JBL factory HU and dash remote that MAlibu was installing back in 2003. This winter I upgraded the system and added the new HU, dual Sony remotes, XM, Icelink, W7, NVS's etc.
Unilink is Sony's brandname for the serial bus connection that thier remotes, MD players, CD Changers, etc. use.
Here is a link to the Crutchfield page describing the XA-C30. Essentially think of it as a hub into which you can plug multiple devices into so the HU can communicate with them. If the link doesn't work just go to
www.crutchfield.com and search for the XA-C30.
http://www.crutchfield.com/S-qmezF2oFmX9/cgi-bin/ProdView.asp?i=158XAC30&search=XA%2DC30 Len