Based on various post on this forum this seems to be the pin layout of the SpeakerLink:

RJ45 SpeakerLink Input on DSP
Pin 1-Master Comms
Pin 2-Ground
Pin 3-RS232 Rx
Pin 4-Slave Comms
Pin 5-Ground
Pin 6-RS232 Tx
Pin 7-AES+
Pin 8-AES-

Since pin 1 was never mentioned I assume it is the comm signal. Maybe someone can test and verify this?
There are 3 different signal with each its own ground. Although both 2 and 5 were mentioned for AES, I guess 2 is for the comm.