I recently upgraded my '09 R56 S to an '06 R53. I had my XM Onyx tied into the factory satellite antenna under the front passenger seat.

My question to you all is this... is there a similar connection to be tied into on the R53? If so, where is it hiding?

Thanks in advance!

 

No.
The stock sirriurs reciever has a different frequency range than xm.
The car was made when the companies were seperate....
Newer anteanas are now commonly dual frequency.