I've been wondering about that, sharing the serial port. On my LDMOS amp project (uses an Arduino Mega, 4 Serial Ports). I'm wondering how I could share ports, if I would just parallel them? I've also considered putting in a relay where every time the Arduino wanted to talk to the K3, that it would first open the relay to disconnect it from the rest of the system.
Have you don this before?
I'd like to take this conversation off-line if you do have some experience with it.