There's nothing special needed to differentiate between serial protocols in kplex. rs422 should work but I've not really thought about 485 and there's certainly nothing in kplex to switch between full and half duplex so short answer: 485 might be problematic if the drivers don't default to what you want. This is definitely something I'd look at fixing if necessary but before I ask you what device/drivers we're talking about here let me clarify what the set up is. Do I understand correctly that you have?
Are you saying the new servers have an rs485 interface and the usb end of the adapter is into the AIS source, or that you're somehow interfacing the AIS source's usb->rs232 with this new adapter?
* Does the messages file tell you that the serial device is being successfully opened?
* If you cat the serial device, do you get any data out? Does it look like nmea 0183 or is it garbled?
* If you have an rs485 device on your new servers, what's its default baud rate?
For serial devices you should be using serial: rather than file:. This will do stuff like allowing you to set baud rate, turning off hardware flow control etc. You probably got away with it before because your serial to usb adapter and hardware serial interfaces were defaulting to 9600 and you don't have too much AIS data.