Tony - this is much more a question for the Mazzoni people than FRS.
Add-ons to any system benefit from the published FRS API and documentation.
But how they implement their use of the FRS interface is going to be a mystery that one would need the Mazzoni information to unravel.
I was told the same thing by Cirro Mazzoni. I have a 6300 and baby loop antenna. I purchased an FTDI USB to Serial adapter. It required a gender change at the 9 pin D-sub. No luck using the Kenwood protocol. Next I am going to try the FTDI USB to parallel adapter. Let me know if you are successful.
73's Bill AF5MR
I have today hooked up a StarTech FTDI USB to RS232 Null Modem Adapter (this has a female RS232 connector and doesn't need a gender bender). I bought it from Amazon UK.
A quick reconfiguration of the loop controller and adding of the cable to my Flex configuration and I now have automatic frequency changing for my baby loop. This will greatly facilitate remote operation when I get onto that!
David G4NRT / Z21NRT