2001 Eddie Bauer backup sensor question

My parents bought a '01 Exp E.B. and the last guy who owned it, ripped out the factory radio. The PDC (or so it's called on BMW's, Park Distance Control, aka "backup sensors") is always off, assuming it's off due to lack of factory headunit. It does have an aftermarket radio. My mom wants to re-install the factory HU. I thought before she bought one, that I would find out if it matters if she can buy any old radio that fits, or if she wanted to keep her PDC if she had to buy a particular one.

If there is a difference, anyone have the part numbers on hand?