Your description of the GLINK-LT says jumpers J3 and J4 can be used to configure for 9600 baud but I can find nothing saying how they are to be configured.

I am using the GLINK-LT in the user port of my SX-64. It is connected via a standard telbbs cable (7 wires) to my PC running BBS Server. Communication between the GLINK-LT and BBS Server remains at 2400 baud whether the J3 and J4 jumpers are on or removed. If I set BBS Server for 9600 baud, the log reports "RS232 error. Framing error! (Check baud rate)".

If BBS Server is set for 2400 baud, all RS232 communication is good with the jumpers on or off.

All testing was done using the Image v2.0 BBS program.

The jumper configuration is on the back of the PCB.
On the commodore 8-bits 9600baud is not supported in the standard kernal (the CPU is too slow to keep up with the bit stream).
The terminal/BBS software must have the special UP9600 driver to take advantage of the 9600baud speed.