My very old MIT Digital Interface has 4 switches.

And, just what do they do?
Here's a question that may stump the panel. I have a 17 year old (according to MIT) digital, RCA-terminated i/c that I recently acquired. It's labeled, "MIT Digital Interface", in blue on one side of its gray "magic box". On the other, are four white side-by-side rocker switches in a red rectangle. Across the top, they are labeled 1, 2, 3, and 4. Underneath them, is the word, "OPEN".
Just what the heck do they do? What do they "open" (besides a customer's wallet)? The cable is so old, even the folks at MIT don't know anymore.
I'd appreciate any help you can give me. Thanks.