The standard 6 CD changer is in the headunit, and I happen to have one you can try if you want.
In terms of the Kenwood, it does depend on how they wired it in, they may have used converter blocks, or as space is a little tight behind there, they could have cut wires to fit everything. You could go down the single DIN headunit route and gain a cubby slot for storage.
Kenwood do some decent headunits for not bad money, so it might just be easiest to get another one with less functionality