However I did have one really big initial problem: the Sony/Synology combo never recognized DSD files. I posted asking for help on another forum and eventually someone posted the solution that even Synology tech help could not come up with:
Under the Synology Media Server -> DMA compatibility -> Enter custom mime type and add "dsf=audio/dsd,dff=audio/dsd" to the box.
Worked like a charm!
I have a Sony UHP-H1 which does exactly the same thing. I've amended the mime type in Jriver so it'll play through that, but it never occurred to me to do the same thing on the Synology NAS itself. I'm going to try this as soon as I get home