That box in the last post is part of the crew briefing system used on Spartan and Warrior. The headsets which plug in to it do not have mics, it allows the guys in the back to listen to the intercom and have ANR but they can’t talk back.
Unfortunately there is no way to use the Clansman kit to do what you need. If you want to communicate wirelessly with someone outside the vehicle through the intercom you’ll need a full 351 or 353 radio installation and the licence to operate it.