hello all. Sorry it took me a while to report back.
So, PSA sent over a new SGCD motherboard with a USB interface which supports Linux bases systems and which works with the Pro-Ject Stream Box S2 Ultra (Streambox), which runs Volumio software. The PSA distributor in Belgium installed this for me free of charge. Thanks Guy @ Aspera Audio.
End result: Everything is working like a charm now.
The Streambox is a fully approved Roon Endpoint, connected to the SGCD via USB. It has a ROON related setting for DSD to convert it to DoP. All other settings are done in ROON itself, including processing MQA sources to a 98KHz/24bit stream which is sent to the SGCD. (Please see below for more details.)
So, in short, using a Roon Endpoint approved streamer is an excellent workaround to the SGCD not being fully Roon compatible.
Roon related settings in the Streambox
Streambox settings in Roon
Signal paths:
DSD
MQA
FLAC 44.1/16
I would like to turn OFF the bitdepth upsampling for FLAC 44.1/16 files, but I cannot seem to find the setting in ROON to do this. Any ideas anyone?
Thanks.