It will inhibit the automatic audio switching so you can hear the monitor tone in the run radio and talk to the run radio contact, while remaining in the automatic mode. But you can defeat this by switching to manual mode and steer the audio manually as you wish. For instance putting one radio into each ear. It also supports the SUB receivers in stereo for working splits if your radio is the stereo split type. There is a stereo mix pot in the logic box to mix some of the audio of each radio into the other earphone since some guys like to listen to a little of the other radio in both ears.
Microphone is supported as well, either PC sound card or external voice keyer can generate audio.
The SO2R Master will switch the audio to the proper radio for you automatically, or you can do so manually. The grounds are isolated. Yes indeed, it was September 1961 when station OH2BH participated in his first amateur radio contest at the tender age of 15. He will be seeking his first SSB all-band honors among his seasoned countrymen and fellow contesters. I just received the SO2R Master today and tried it out.