I've heard some good things about this scosche DIC dash kit (they call it a GM LAN adaptor). There is a pic as well. Trying to find one locally so I can check it out before buying. At any rate, it doesn't appear to be as cheaply made as the metra.
Cost = $200
http://www.scosche.com/scoschesearch.aspx?qString=g6
Cost = $200
http://www.scosche.com/scoschesearch.aspx?qString=g6