Add a section in the Gentoo Linux ALSA guide about enabling SPDIF and surround sound support. Reproducible: Always
If you can provide some instructions on how to enable it, we can put it in the guide. I don't believe any of us use SPDIF. In theory, it shouldn't be hard . . . it should just be a matter of setting the correct volume in "alsamixer", usually the IEC958 control.