Tom, I've got a LCX27 too but don't use any interfaces. That appears to be plain ole RS232 type info. If the protocol is the same it may work if its in the same format. But thats what Lowrance is telling you. If you have access to a serial printer you could print the output from each and then compare it. Or just set both to the same baud rates, plug them up and see what happens. I believe send and recieve has to be swapped on one end of your cable but I can't remember for sure.
If no serial printer you could send the info to your laptop if you have a serial port on it. All you need is pins 2&3 for send/rcv and 7 for signal ground.
Man, you are really taxing my memory on this stuff.
Fair Winds and Following Seas
Bill H. PTC USN Ret
Chesapeake, Va