Replying to myself…
Seems there is a new device that does exactly what we need here: http://www.transvinyl.com/index_en.html
I sent off an email to Trans Vinyl and received the following response from Jörg Schambacher:
“…What is described on the Roon Labs forum page (this thread) is almost exactly what the TVL1 can do. The box can provide a HTTP based OGG-stream with FLAC audio containers in the streaming mode. We have never tried it with any Roon equipment so far, but it worked with the OGG/FLAC capable equipment we have tested.”
I know very little about the TVL1 apart from what’s on the linked web page, but it is certainly an interesting device. I’ll respond to Jörg Schambacher later tonight and ask him if he’d be willing to inform us directly in this thread.