OK I did alot of looking on this & there wasnt much! So I figured I would Post up & Tell ya what I found out & How I did it! I Did the Steering Controls to with Swi-ps so they work!
Thanks to LsjPup (Josh) For the Help to!
1) Yes you can Use the stock xm entenna at Least on the 06 Balts!

2)Remove the back Deck Panel! Can Be Fliped forward with the belts still attached)

3)With the Deck ReMoved, Between the 2 back Speakers is the Module for the XM! SeePic Below! Mines is the 1 on the Right<<Stock 1 is bolted in on Left!


4) The Greenish Brown Plug is the XM entenna (Disconnect it!)


5) Now I have a Pioneer Radio & Xm ! MY Xm Plug is Pink >> Not Greenish Brown, The Built in groves on the Plugs are just Slightly Different 1 Matches & 1 Dont! Simply shave off the 1 that doesnt Line Up with a Razor Blade!
If you Look in Pics Below the Pink is LIL Fuzzy>> But You can See that the ridge on the Bottom Right is still there!


Now Just Simply Plug in your New XM module & run Your Wires its Hooked-up!
I mounted Mine in the Trunk See Below Pics !



My Radio!