Crosspoint switch matrix for audio frequency signal?
Uso 4066 analog switches. These make perfectly good audio analog switches (See This) and have been used even in high-end audio (my old Quad 44 preamp uses similarily specced chips). These have been around for a long time and there may be better moderen equivelents. You would need a good few to build up a large matrix but they are easy to drive from ttl/cmos, 5v/3.3v etc.