According to this website, there are already compiled, working versions of Volumio supporting SACD Iso playback.
Not owning a Baidu account myself, i haven’t been able to download and try them.
If anyone has a Baidu account or is fluent enough in Chinese to contact the blog owner and ask him if he could upload a copy on Mega or other websites, please be my guest.
Latest version seems to be volumio-2.457-2018-09-17-sacd-q2m-pi.rar
I believe it is using manisiutkin’s mpd fork.