What do the outputs look like on them? I am going to assume that they are little mixers intended for live remotes. Back in the seventies and early eighties when I started in radio that’s how you did live remotes. We used Shure M-67 mixers that had two terminals on the back and you would call the phone company and set up a Dry Pair that was a signal pair with no voltage on it that would be connected to the remote location and terminated back at the station. We had several dry pairs along with al the incoming phone lines tied back into engineering and all the dry pairs would show up on a patch field as just Tip and Ring and we would manually patch them thru to the studio that they were going to be used in. At the remote end there would just be a telephone line terminated into a block that we would attach to the mixer output directly. Because it was a balanced system and unless you had an issue with the phone line itself it all worked very well with good response and no hum, sometimes you would get a ground on the pair and when you did a test at the remote if that happened you would call the phone company and they would come and switch you to a different pair. And for all of this support by the phone company the station paid about only $6 per line to have it installed and operational for that remote. Back then engineers would go to the remote site and set everything up for the talent and also require at least one other engineer back at the studio for testing things from end to end. Once the phone company got out of the dry pair business we went to dial up remote mixers, small solid state mixers with a rotary dial or touch tone system or VHF/UHF remote Marti systems. Today most remote operations have migrated to digital systems that work across cell networks or TCP/IP systems that work over the internet.
Some of my first jobs in radio were setting up remotes and patching them thru back in engineering. The station that I was at back then had an Air, Interview, News and two production studios for the AM operation and a dinky little studio for there FM
I did some remotes for a college station in the 70's. I guess the M-67 were acceptable for the technology of that time to use for remote mixers, but I wouldn't be 10 feet near those things now. Shoved the audio down some pair of wires from the 'phone company. Really didn't sound that bad on the air. They switched the board to mono and no one knew the difference.
Fred