Bose CD player head unit

If you've read my last thread, i talked about redoing my bose stereo system in my car. Well, i gave that up, many people suggested not to do it, because of the integration, and having to redo all the wiring, and everything. My question now is about a new bose head unit. I have been frequenting ebay and other resale sites, trying to find resale bose cd players that i could replace my old bose cassette deck with. I am wondering about the compatibility of other head units with my bose system. Is a unit still compatible if its for a more recent model of car? I'm not so much worried about the physical aspect of the fitting, i will take measurements and make sure the dimensions match up, but i am wondering if most of the units out there would work with my system. I appreciate any comments, and advice you have, thank you.