Audio Systems: stereo and PA system replacement, radio cuts, warranty details

Question
I drive an 18 passenger bus that has an aftermarket am/fm/cassette installed in the dash.  Connected to it is a pa system that works through the radio.  It has its own volumne control. When you press the button on the mike to use it the music from the radio cuts out.  The cassette no longer works and I am trying to replace it with an am/fm/cd player but keep the pa system.  Three car stereo stores looked at it-two said they would have to find a stereo that allowed the mike connection & cannot locate one.  The 3rd said no problem, they can install a $95. player and use "whatever is in there" to make the mike hookup work.  Who do I believe?

Answer
There are a few ways to do what you ask.
BTW, the cassette player quite probably just needs a new drive belt.
As to replacing:
To be honest, I would go with the 95.00 job if, beforehand they will explain how it works and what hardware will be added as well as device warranty details.  Any reputable shop should warranty their wiring work for the life of the vehicle.
But you should first talk to the reps at crutchfield.com and tell them your situation.
I am sure they can find a resolution for you and then you will have a reputable second opinion as to what you are really needing based on hardware which is currently available and/or compatible.
http://www.crutchfield.com   1-800-319-8264

JM