Have a look at Squeezelite (on the streamer) LMS (on the NAS/Pi) and iPeng controller. IPeng is really very impressive in terms of feature list. LMS is also exceedingly able (upsampling etc.).

IPeng cost £9. The rest is free and may get you 97% of what you’re after.

Also RPi plus Allo Digione Sig plus good power supply would possibly more than hold its own with 818v3. SPDIF output so plug and play. A little fiddling required setting up.

Roon is fab and great for manufacturers, do I need synced endpoints, not really. Very convenient if you don’t fancy a little fiddle. SQ? I though SQ improved when I went RAAT, I’m now just double checking before cancelling Roon. More features than I need.