The module is the part of the radio that holds the memory and where you put your frequency chips in, unless you have the novak module then it has the extra reciever and you can jus turn the dials to choose your frequency, no crystals required.
Get the M8, fm 75mhz, your current receivers will only work if they are airtronics receivers, or if you have any novak receiver that is an airtronics style.The M8 is a great radio, and you can store up to 10 models in this radio, so you will have no problem running your three cars from it.