Unless you are specifically sending RossTalk commands from XPression the the GVG frame (probably not) - you don't need to input the GVG frame IP anywhere in the XPression config.
Just create the RossTalk board in XPression, set to TCP and the port number the GVG frame is using and make sure the RossTalk board shows as "active" in the XPression hardware setup.
RossTalk is a fire and forget protocol. It does not send success/error replies back to the originating device.
Can you ping the GVG frame from XPression? Is port 7788 open? Is your firewall turned off or have port 7788 open?