Porsche: XM satellite availability in 2005 Cayenne?

Hi,

I have a 2005 Cayenne S, and the PCM manual indicates that either XM or
Sirius is available. But, it appears to me that only Sirius is available:
the Radio ID has a 12-digit number (rather than 8, as XM requires), and the
XM website indicates availability in 2006.

Does anyone know if the manual is just plain wrong?

Thanks!