Icom CAT/data modes cable

I bought a data cable for Icom HF transceivers from the Blackpool rally today. It's something like the Icom IC-Cable-8 (cable 8 on this page).
The cable I made myself used the 6-pin mini-DIN socket on the IC-7000 but this one uses the 13-pin accessory socket and the 3.5mm jack (CAT interface). This replaces separate CAT and PTT/audio cables, freeing up a serial port.
PTT is possible via both CAT and serial port (RTS line). When using the 6-pin socket, there was no transmitted audio if CAT was used to key the radio (so there is no need for the hardware PTT circuit anyway). This doesn't happen with the 13-pin socket but there is one problem, the microphone sockets aren't disconnected. So when operating data modes using this cable, the mic gain needs to be turned to 0. If there is someone keying up with no modulation then it's probably me forgotten to turn the mic gain back up for voice.
The level of the PC Line Out also needed to be turned up from 10 (using my 6-pin cable), to 25 (using the 13-pin cable) to get the same output power.
I also got a Snowdonia Radio Company 9:1 Unun