Here are some things I've found using the rear 13 pin connector on the TS 2000. These are not in order of importance, or discovery.
The send button on the front of radio will not use the rear audio.
The mumble server must be stopped before the sound-test programs will work.
Menu settings that seem to work....
Menu item 41 is set to MID which is the FM Mic Gain
Menu item 46 is set to SUB which is the built in TNC.....set it away from the main radio
Menu item 50 is for the PACKET... which really is the audio input to at the back of the radio..
50a is off .... which is the packet filter bandwidth setting.
50b is set at 3 .... which is the mic audio input level on the rear connector
50c is set at 4 .... which is the audio output level...for the main receiver
50d is set at 0 .... which the 2nd receiver audio level out the back
50e is set at MAIN .... which sets which transceiver to use, the main dial or the sub
50f 1200 baud .....is not relevant
Menu item 55 is set OFF for Packet operation
Menu item 56 is 9600 bps .... which the COM port speed. which should match on the rigpi the settings->advanced radio->baud
I did have to turn on in RigPi, the PTT setting in Settings->Advanced radio->PTT to ON while transmitting
Otherwise the CAT control commands to transmit are used, and it will key up the transmitter, but not use the correct audio source.
I have found that there is plenty of audio that the rigpi will produce. my mixer setting are all well below max.