Looking at PC-connected mixers as a way to augment my KVM based on a suggestion from a reader. Hercules DJ Console USB DJ/Audio Interface for PC — this will let me mix the output from one PC (acting as a usb sound card) with (it looks like) an spdif output from another pc. I can’t totally tell from the specs but software like PCDJ may do this all in software — route the audio output from one pc to the capture interface of the other, and then mix on the pc. Of course at a CPU load cost. I am sure some of these other mixers have some remote interface tho it is hard to sort thru them all.