You basically gave the required info in the second post of this thread I think Mark.

Code:

---

[hijack]
extmute_on=Hush
extmute_off=Hush

---

should work I think however there is potential for it to get out of sync if the player isn't running when extmute goes active. Alternatively some kind of "Volume+, Volume+, Volume+, Volume+, Volume+" (and appropriate Volume- codes) sequence would work although it would suffer the same sync issues possibly.

As for actually getting the line to work, from memory it will default to the low/GND state i.e. applying GND won't do anything - you need to apply +12V to see anything. Have you seen this?