Most excellent news – much appreciated.

I dusted off my Parallels / Windows 7 VM and updated Sooloos Configure and off it went. One word of warning: upon clicking the MS600 in the window, it immediately started updating – no warning (do not turn off), no progress bar – just showing the MS600 in 'boot mode', the indicator lights on the MS600 itself lighting up like a christmas tree.

After a few minutes, it showed firmware version 164 – and it's happily streaming Roon now.

Living Roon: MS200 > Reviver > MiniDSP DDRC-22D Dirac > DSP5200 | Headroon: Allo USBridge / SBooster PSU > Prime / SBooster PSU > MrSpeakers ÆON Flow Closed | Bedroon: Bluesound Pulse 2 | Roon Server @ NUC6i5 on Debian Stretch