After spotting the guy on gootube who said it took only 3 hours to make a USB audio device out of an STM32F4, the decision was made to do it.  The TOSLINK cable evolved out of a need to use the Yamaha intact & defeat power line noise, originally.  The black & green boards were the parts from the Yamaha required just to go from TOSLINK to analog.  

A custom USB board would be the most efficient way to expose an I2S output so the audio could be sniffed & go to 96khz.  A big win is being able to plug it into a laptop or a raspberry pi.

Sniffing audio with any software solution wouldn't allow mixing it in a headphone monitor.  

192khz seems rather pointless for its use.