I set my IO-4 board to:
Serial A
0x20 Data Port
0x21 Status Port
9600 baud, N,8,1
It seems to partially work. The boot loader text displays fine, but then the computer seams to struggle and start to output junk. It never prints the dots or starts to load the SD contents. I have attached a photo of the screen. If I revert back to the onboard SIO all is fine again.