anyone know anything about the discomate studio cue system ?

I got given a couple of "discomate studio cue system" headphone amps probably from the 70's I'm guessing.  They are on wheeled stands, & have a round military style connector on the bootom of the stand, the connections going through the pipe work of the stand.  It looks like you can send 2 mixes which can be blended in the unit & each unit will feed 4 sets of headphones.

I'm just wondering whether anyone has any info on the system, because I'm trying to make some use of it ?