i think the XM occupies the AUX. I hear if u install stuff in the AUX port, u lose ur factory XM, so I guess... if you dont use ur XM, ur free to unplug it and whenever u push on the XM button/AUX, it'll revert to w/e thats hooked up.
yeah, the connector is a bus connector tho so you need a soundgate adapter....search and you will find more info than you can handle.
i have one and it says "CDC" (cd changer) on the screen and i run my ipod through it.
i think there is a Y cable that allows you to keep XM