Custom kernel development (aka SPDIF on Udoo Quad)

I’d like to try and get SPDIF working on my UDOO quad with volumio. There is page about how to enable it on the UDOO forum here:

So, I need to recompile the kernel to get this enabled. How do I go about doing that? Is volumio using the kernel from here?

I have found the kernel files for volumio udoo on github here: … /udoo/boot
Any ideas how I would get an existing menuconfig file for the kernel so that I can make it as close the the existing volumio kernel as possible?

Is the volumio kernel custom? is it it based off an udoo distro somewhere?

Any info would be greatly appreciated. Thanks!