Connecting two moOde boxes

[Sehnsucht]

I have two mooode boxes and I'd like to connect them.
1) pi 4, usb hard drive with a lot of music, ethernet
2) pi zero w, sd card with a little music, wifi

Both work perfectly independently. 
I'd like to use device 2 to listen to the music from device 1, using PEQ.  I've connected 2 to 1 using samba and...well, it's taken maybe 30 minutes to index all the music and it's not finished yet.  I imagine it'll do this every time I reboot device 2.
Is there some way of achieving this with some combination of UPnP DLNA?

I can listen to the music from device 1 using UAPP on my tablet just fine - I just navigate around the share and play tracks, add albums etc.  It just works.  So an alternative would be if moOde supported a "poke around the samba-shared files live" mode which didn't required the files all be read into an MPD database first.

It would be very odd if after you rebooted the Zero MPD would initiate a database update. That never happens on any of my systems.

The long update times are prolly due to slow Zero, slow uSD Card, slow Network etc

I left it running for hours and eventually it finished.  And it's true, it didn't seem to need to do it all over again after a reboot.  I managed to play a few tracks from a single folder without issue, which was great but then I tried to play another album and it just kept hanging for minutes at a time whenever I tried to navigate and play, and never actually played anything else.  Each time it was hanging I could, eventually, connect via ssh or samba so it never actually died.  I suspect a pi zero over wifi is just not up to the job of dealing with large (tens of thousands of tracks) mpd databases (despite having already dealt with it to the point that I could play anything).