If it has Bose, it has the 6 disk changer. If it didn't have Bose, I'm fairly certain that they came stock with a single disk player. They are interchangeable though, and you don't need Bose to swap a 6 disk changer head unit. The difference is in the speakers and external amplifier.
As for XM, the answer is 'Yes' with a caveat. XM wasn't an option until mid '03 when the dash switched to Black. I found out the hard way that the pewter dash radios (including the Nav) do not have the XM firmware. My newly retrofitted '05 DVD Nav does. It was plug and play with no programming necessary with the Radios and More kit.
-1- was the pioneer who worked with them to get their kit to work with the CTS Nav system. I was the second one to purchase the kit, but after looking at schematics figured a cheaper way to get the same thing. The write up is at CadillacFAQ.com, which describes how to build your own harness and save $100 on the XM retrofit.