So a comment on @chouston 's post, and then an update on my previous post.If I remember correctly, the Comstar system uses to channels with up to 4 units per channel, and those channels can be run separate or conferenced.
Each headset is numbered, and they are programmed to work on channel 1...
The church where I am taking over as Technical Ministries Director got a set of 8 Comstar single and dual muff headsets (not the beltpack style) about a year ago.
3 of them are no longer working, one after about 6 months. The microphone quits so you can hear but not talk. (I may actually leave...