Thanks for the additional video, that really takes me back.
That rack & carriage looks very similar to the ones I used to service, but also a bit different. The optical seek system must be a newer development, or did you DIY that part?
As you may know (and if I remember correctly), back in the late '60s/ early '70s, NSM used a real magnetic core memory for record selection, using tiny ferrite cores & wiring just like the computers of the day. But after a court loss to Seeburg, who was using the same type of system, NSM had to revert to a motorized sliding pin arrangement under the rack, which was a step backward technologically.
That's the reason I asked about yours - the mag core setup relied on a faint 1 uS pulse from the cores to detect the selected positions in the rack, and might have been more of a challenge to DIY, heh.
As for the topic: I've been wanting to throw together a simple analog quad "vector-steering" circuit to use on the front end of an old dual-channel CRT scope I no longer use at work. But awhile back it occurred to me that I no longer have an easy way to connect something like that to my system! Everything is digital right up to the power amps, with separate analog outputs for each woofer, tweeter & midrange coming out of a pair of miniDSP nanoAVR-HDAs (see avatar).
I'll have to keep any visualizations in the digital realm, since that's where the audio lives for the most part. Not that I'm complaining - I absolutely love the sound - but things sure ain't as simple as they used to be!
Oh well - another reason to get back into coding, which I've missed.