Radio Design Labs AMX-84 Audio Switcher and Control Panel
I suffered using an old hi-fi amp to do audio switching for far too long. The lower of the two units here is an audio matrix switcher. It cost a total of about $120 on Ebay. Any one of 8 inputs can be summed into any one of four outputs. The channels are selected by closing contact pairs, and the upper unit is a 32-way homer switch panel for this purpose. No more scratchy noises, no more wiggling the switch when a channel starts fading in and out. The summing nature of this switcher allows more monitoring flexibility too. The internal design is delightfully basic using good ole CMOS switches and TL074s. If I was going to design an electronic switch matrix, there would be no point, because this is exactly it what it would end up like, though I'd have an LED for every switch and not just the input channel activity.
Bonus points for insulation tape rainbow colour coding?
I believe there is a B version with an RS232 connection for interfacing with a computer.
Rear Detail Of Control Switch Panel
Wiring, showing the use of chopped-up domestic JVC phono leads from Currys for the audio input and output.