Unique Headset Requirement, any solutions?

I hate to create another thread about headphones, but I think this is a unique problem without an existing solution. I'm coming to the Goodjers for ideas...

I need to simulate a vehicle crew where 5-6 members in the vehicle can communicate with each other freely over the headsets, all the time, without any push-to-talk. However, any one of those stations can also push-to-talk to communicate on at least two separate voice nets. I need this to be a single headset solution and I would like to simulate up to 6 of these vehicles on a local network. So, the commo between clients in one simulated vehicle obviously should not be heard by another simulated vehicle, unless it is over one of the push-to-talk voice nets. Ideally, selection of which voice net is done with a hard switch and not with software.

Are there any hardware or software solutions that would allow this?