For my e46, you offer a radio upgrade that looks like the cd53. There's an upgrade to make it play mp3s and whatnot. What is that? Some sort of software upgrae to the player? Is it a different model completely?

The "model" is the same. The later model pieces just can play MP3/WMA "data disc". Essentially a "software upgrade inside the head unit.

Works great and looks 100% stock, because it is :)

Thanks for the info. You wouldn't be able to tell by the model number on this:

http://forums.bimmerforums.com/forum/showthread.php?t=919366

If that's one that can, would you? I just bought that from the guy and am curious :) I appreciate it

Ask him the build date of the vehicle it came out of(If it was the OEM radio in that vehicle)