Here are my settings:
Type: Inline
Model
RO-107
Role:Signal
Run:Running
Serial Port: COM12
Baud Rate:9600
Data Bits:8
Stop Bits:1
Parity:None
Park:855.6875
Mode:FM
EDACS96
Your Com setting for the cable is fine, I use Com ports 11 and 12 all the time with UniTrunker with no problems. It doesn't matter what frequency you use for Park on your signal receiver because it will be busy listening to the control channel. Now, if you use voice following with a second receiver, then you need to set that Park frequency to some quiet frequency nobody is transmitting on. I use 851.0000 myself.
What I'm wondering is, maybe you need to set the baud rate from 9600 to 115200, because that's what the PSR-500/600 and Pro-106/197 use, and I think that if the Pro-107 is built off of the same GRE manufactured platform then that's going to be the setting you need to use for your scanner. I couldn't find anything about it in the online manual, so I could still be wrong.