[Link: chicago.craigslist.org]

I'm not sure the internet even existed when that was produced.....

I'm sure, and NOT.

Per [Link: beoworld.org], it was made from 1989 to 1991.

The CD sticks sometimes. Be still, my heart.

No networking, no USB, no WiFi. There is a proprietary wired, multi-room control capability that was advanced at the time. The handheld controls are IR. I’m surprised that the speaker relays are not heckling the user. By the way, the IR uses a 455kHz carrier.

In my opinion this unit would have nostalgia value only.

Any idea why 455 kHz was chosen?

Not really, it was the B&O engineers being B&O engineers having a different take on things as they tend to do. I think that they wanted a higher carrier frequency so that they could more easily design filters and be away from the 40kHz crowd. 455kHz allowed the possibility of using commodity parts designed for AM radio IF strips.

Maybe this.
Well outside that range, 455 kHz modulation of IR beams seems to be used exclusively by Bang & Olufsen (the Danish manufacturer of upmarket audio products). Standard parts for this modulation band are becoming difficult to locate. That allows data transmission at about 10 times the rate of other current IR protocols

It's amazing how many of those things I ran in to when I first got in to this business back in '94.. Even ran in to a few of the whole house systems they made with the long horizontal wall mounted keypad. They were a pain in the ass to work with though I have to say they worked better than any of the Bose units I ever encountered.

Whole house control took B&O by surprise. Standard IR extenders of the era (and there weren’t many) did not work with B&O. Dealers were ordering replacement B&O IR receiver boards and building them into walls and furniture. The factory was concerned that there was a massive field failure problem, but on investigation discovered an opportunity. MCL (Master Control Link) was born. In my opinion, for a brief while, it was the most viable, whole house audio control. Yes, it was quirky and closed, but it was attractive and always worked. Other ideas were out there, but I didn’t think that having a dedicated PC running things was a great consumer solution. And, the competing remotes and keypads were crude. B&O was slick and offered good training and support. Unfortunately, before long it became clear that B&O was thinking “silo” and everyone else was thinking “universal”.