There was a time when being an audio enthusiast meant living with wires. Lots and lots of wires. That was the price you had to pay for quality audio, especially if you wanted a home theater system ...
Here is a multi channel audio mixer circuit based on 2N3819 n-channel JFET. It mixes as many as inputs into one channel. The design seen in the diagram is for only two channels (stereo into mono) but ...