Do we all agree that a crossbar topology is a good solution?
Target is 50 in and 50 out.. but that's a little flexible.
Input signal levelup to 20 Vptp
I thought you could use this https://uk.farnell.com/vishay/dg445dy-e3/switch-analog-quad-spst-soic16/dp/1102506
depending of course on price
What about digital approach? On each input one ADC, sample it and send data to corresponding output DAC.
.For 50x50 it will be awful lot of data to send. Surely out of reach of simple protocols like I2C. But maybe some modern protocol such as Gigabit ethernet or VDSL? I don't know how they are implemented but they are able to send lot of data to lot of devices.
I can understand why someone needs a mixer, to have many inputs routed into audio path. But why does someone needs 50 outputs?