Wanted to post to make folks aware of this issue:
https://github.com/raspberrypi/linux/issues/888
which causes some high-speed DAC’s (including my Schitt Modi, apparently) to be unusable.
I’ve been able to fix this issue in Volumio by downgrading the kernel to 3.12, and it looks like the issue will be resolved in kernel 4.14:
https://github.com/raspberrypi/linux/pull/1094
So far, Volumio seems to be working with the older kernel, but if anyone knows of issues, please post.