I replaced the "standard" cd changer with a Sony T70 MP3/CD Changer. (I havent got the standard HU though).
You'll need a Connects2 adapter to convert the changer lead from the stereo to fit a sony changer.
Only restriction I can think of on the Head Units is they only handle 99 tracks per CD, you can't navigate folders (probably can't input a track number) and won't display the ID tags, but no other
problem apart from that!