So it appears that my deduction from the pictures of needing a cable swap was correct, however, it turns out that the installed cable was actually the normal RS232 and what we need instead is the RS232 null cable. After the swap was done, the communication between c1vac and the XGS600 controller became active. Although, the data makes it all to the to c1vac without any issues, the scope view of it shows that it is mainly utilizing the upper half of the voltage range which is just over 50% of the available range. I don't know what to make of this.
I guess, the only remaining issue now is the incorrect atmospheric pressure reading of 1000 Torrs.
Following repeated failure to establish communication between c1vac and the XGS600 controller via Perle IOLAN serial device server, I decided to monitor the signal voltage of the communication channels (pin#2, pin#3 and pin#5) using an oscilloscope. The result of this investigation is presented in the attached pdf document. In summary, it seems I have used a crossed wired RS232 serial cable instead of a normal RS232 serial cable, so the c1vac read request command is being relayed on the wrong comm channel (pin#2 instead of pin#3). I will swap out the cable to see if this resolves the problem.