The "links" won't do anything useful without a B&O receiver as the head end. Fortunately, their signal distribution was mostly speaker level and you can just bypass the links. Probably you have the MCL2. If so, you'll need to follow the gray wire from the wall mounted unit to the gray box. The gray box is essentially a relay box that drops speakers on the line. There are also some amplified links. Anyway, you'll need to dig out the box and patch the speaker wires. BTW, these are not general purpose IR receivers, they only deal with the B&O IR commands that are 455kHz, not the typical 38kHz. IR commands are decoded in the gray box, then sent over the white shielded wire as B&O specific (2-way) commands. Obviously, all of the rooms play the same program.

If you are lucky, you could replace the links with wireless Sonos CONNECT:AMP's. If you are unlucky and I was the original installer, probably not, because I usually dropped the relay box into the drywall and CONNECT:AMP's don't usually fit inside drywall. If any of the wall mounted units are surrounded by a trim ring, that ring is a "pass through kit" and that's how you pass the gray relay box into the drywall. (otherwise the gray box is too big to fit through the mounting hole for the controller)

It is possible to pop the wall mounted controller out of its mounting shell without trashing everything (you may break a tab or two at this age), but one must be gentle. These are two piece units. First, one mounts a plastic shell in a drywall cutout, then the controller is snapped into the shell. You must carefully pry between the shell and the controller. Don't pry between the drywall and the shell. Once you get the controller out, there are two mounting brackets that sandwich the drywall from behind. WARNING: these are similar to toggle bolts, don't completely remove the screws or a piece will drop inside the wall -- you will regret this unless your intention is to remove, patch, and paint. You'll notice some oddly shaped slots in the back of the shell that will allow you to loosen the screws, then rotate the clamps 90°, releasing the shell.