You could look at military surplus headsets and jboxes. ( junction box). It slows intercom, multiple radio monitoring and ppt for outside vehicle comms. I adapted a setup from a tracked vehicle for my contact truck at work. ( hummve with amassive snappon toolbox). The 6.5 in the hummve makes it hard to hear with the normal handset when your driving at speed. The headsets are pretty comfortable and the only downside is the ppt box on the cable. It is kind of bulky. This stuff usually uses a 5 pin twist connect or push lock, but I've also spliced in an aux cord for auto paused music on the go. Done improperly, it will broadcast whatever you are listening to. Just an idea