DAC+ DSP Toslink input to RPI

I'm trying to get Toslink PCM audio into the RPI.  This is the entire reason I purchased two of these cards.  This is for capturing TV audio for distribution using snapcast and/or Linux based audio filters run outside of the DSP.

I have Sigma Studio up and running and have successfully written a profile to the DSP using it.

Responses to the second question of this post mentions a 'hifiberry-dacplusdsp' dtoverlay which supports reading data from the DSP to the RPI, but does not expand further. https://support.hifiberry.com/hc/en-us/community/posts/360006995438-HifiBerry-DAC-DSP-192k-Processing-Path-and-SPDIF-input

I'm guessing perhaps I need ASRCout, but don't know much beyond that.  I'm an electrical engineer by degree, took some DSP classes in school, have been studying ALSA, but I2S is foreign to me.

A kick in the right direction would be very helpful here.  What outputs in the DSP must I route the signal to?  Where am I looking for the data in the RPI?  Approximate steps to get the data into a named pipe/mkfifo appreciated.




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