if you want to stay compleatly gm, there is the PAL(personal audio link)
I have seen them in other gm applications and they work pretty good.
you get song title and playlist title on sreen. only able to seek thru song list one at a time, same with playlists. uses the xm2 band on stock radio. but you do have direct control opptions. also has a aux input. Dealer install is retarted, but there are custome harnesses avalible also.

hope this helps.
Phat Pat