Got the invite (P #32XX) and figuring out whether I want the upgraded stereo option. Sirius XM isn't a huge deal, but I'm not sure what difference the sound quality makes with amp, subwoofer and 16 speakers. From what I understand on the S, it is a difference between 12 and 7 speakers (plus a sub). Thoughts? Also, I have Sirius XM subscription from my wife's car that I can access from my iPhone. Can I just run it out the phone and not worry about getting Sirius for this car?