Those look a lot like the wiring (that was) in my grandmother's attic!
I suspect the house has been rewired by now, but when I saw that wiring 30+ years ago, it was at least 30 years old (probably 50) so if it can work as AC wiring, it is probably safe for audio.
To elaborate, this wiring in the attic ran between ceramic insulator stand-offs. By the time I saw it (and probably why I have a pretty good remembered image), the fabric was looking pretty dry and seemed like it might break open/off if you abraded it! I kept a distance. The image makes me think fiberglass, but I'm not sure fiberglass was common that early, it was probably the fineness of silk threads that I saw.
I wonder how much money someone could make retrofitting amp wiring?