Responding to myself…
Datasheet reports 7.05 idle watts (~11w at active random read) so depending on what it considers idle, it’d be 8*7.05|11= 56.4:88W
Server clocks in at ~102W. Halving the drives would reduce the power by 27 : 43%
And in theory other components (motherboard, CPU…) must be using anywhere from (102-88) :(102-56.4)= 14 : 45.6 W.
Anyone with Navidrome should consider trying this. It provides a means to create & modify the smart playlists graphically & makes it easier to rate songs with stars vs the web UI