Take note of the dash mounted unit and get another one from this forum. All of my audio problems in the past have been solved by swapping in another head unit, so that is where I always start.
When I was in need, I got a lot of help from Rubydist and SV&HODan who knew all the models, and what ran what. Another big help came from Cutubitus (?) who had all the faceplate choices of the different models and all the schematics, as well as pictures of his install from a recent dash change.
There is a fair amount of information on this forum, and lots of illustrations in the threads to help you along.
When the original system is working properly, it is hard to beat, and it is nice to keep that dash mounted control unit.
If you do go for a new system, there is a whole different set of wiring built into the car that you will be using.