Hang on to the working SVX stereo but leave the Kenwood in place.
I've had a total of 6 Svx stereos and all have failed in some way. Usually the laser in the CD player goes but there are other issues with the cassettes as well. They are a minimum of 20 years old and will die sooner or later.
Buy some good replacement speakers for the doors and rear deck too. The old stock speakers are poor even when in good shape. After 20 years in a car they begin to deteriorate.
Try
http://www.crutchfield.com/S-LaPBTakVAfd/
Does the Kenwood have a working SVX cover on it?