If one of the cabinets says 200D then it is probably a hybrid system with a digital brain but also utilizes analog cards. This will support a dataset for PBX interface (I always used the "stand alone" 1103 for this - works fine.)

Still that is not the issue here (at least yet) it is the CAS interface. Again I would try running a cable directly from the digiport to CAS (eliminating the existing Y cable). It could also be that on the serial side programming on the digiport there is a flow contol issue.

Do you have a laptop or desktop with serial port connectivity available? If so you can do some testing on the serial port side.

A lot of times the Franchiser looks at the whole PMS situation as just another revenue center. I could possibly see the advantage of doing the interfaces via IP to a central location if everything were done that way - Terminals, printers, etc. But you obviously still have a lot of hardware that you can't administrate. Just seems to create more problems than it solves. Especially when the support people aren't as knowledgeable as they should be.