Please give advice on this idea

Hello, I was wondering if I could please get some help. I have a 1993 Accord, I have replaced the stock radio/tape deck with a very simple one which was given to me for free by a friend. I was wondering if it would be possible to hook up my stock unit aswell. I was thinking about hooking up everything to the same, as in hooking up the wires on the stock unit to the one on the new one. That way they could both output to the same speakers and use the same wires. I would apreciate any insight on this since I need a tape player for some old tapes which I own and cannot find in cd format. Also, I was thinking of placing it in the little box underneath the origional unit, I still have the box attached to my new cd player, but was wondering if I could romove it and put the old deck back in instead. By the way, I would never turn both decks on at the same time. I would turn one off while using the other one. Or I could always put a switch on the ground wire so I could control which one is turned on, that way I would not turn one on accidentaly. Any help would be greatly apreciated. Thanks again, Nick.