Cadillac Cts 2004 - Carputer Project, you didn't have to go over to cadillacforums to find him. I believe Smeesseman did a full write-up on his install complete with details on mods to the CTS. AfterDigital has a sweet install as well.
Where are you located? Maybe one of them will see your post in a month or two and chime in. Their installs have been so troublefree, they rarely visit.
I'm starting my install in my XLR-V in a week or two but its a whole different animal.