I don’t know much about DSD, but if foobar intends to support it over UPnP then it’ll have to advertise the capability.
foobar currently advertises support for:
http-get:*:audio/flac:*,http-get:*:audio/L16:*,http-get:*:audio/x-wav:*,http-get:*:audio/ogg:*,http-get:*:audio/x-ogg-flac:*,http-get:*:audio/mpeg:*
I don’t know if there are official mime types for dff/dsf/dsd, but going by this post it looks like Symfonium expects:
http-get:*:audio/dsd:*, http-get:*:audio/x-dsd:*