R1MAN

The CD player (5 CD changer ) in my LX450 gives me a lot of problems, I mean all of sudden it stops plying and goes to radio, anyway I took the car to one of those audio system store, and after they checked it out they told me that the CD changer works fine, and the the head unit or receiver might be the problem, and they have to take out both, CD changer and head unit, out to fix it, and its going to cost 300$, on other hand if I want to buy a new set it'll cost me 500$ installed, which is I want to do, get a new set.
so I was wondering what system do you guys recommend?
especially I need something that the CD changer can fit in existing place, which under the arm rest, and the head unit wont have any gap, and it can fill the whole area.
thanks in advance.