Many of the Intercoms have a "Music" channel input which boosts the volume much higher than the audio output from comm radios meant to drive headphones directly.
On my Sigtronics, the volume was much too low on the radio input (which would not have provided automatic muting upon receiving a radio call), but the music channel was actually too loud so I added a potentiometer to control volume. That way I only have to use the rocker switch to set "max volume" once on the x96, and can dial volume up/down easily on the panel.