Volumio 2 is Debain Jessie based where only miniDLNA 1.1.2 is available. It does not support DSD.
Volumio3 will be based on Debian Buster and will get miniDLNA 1.2.1 as soon as my PR on GitHub has been reviewed and the plugin been merged to the Volumio3 plugin store. Unfortunately miniDLNA 1.2.1 does not support DSD, too. 
miniDLNA has DSD support only as of version 1.3.0. miniDLNA 1.3.0 will be available on Debian Bulleyes based systems… so depending on if and when Volumio switches to Debian Bullseye, it might take a while until miniDLNA with DSD support becomes available.