oof a real question let's see
I think the "correct" solution for this will matter less about the hardware setup and more about how you want the software to operate. To be honest I still just kind of either use an MP3 player or Sit Down At A Music Device to listen to music, and I've never had a place big enough to start worrying about making music happen in multiple locations. Apologies.
Obviously the storage back end can just be TrueNAS running on whatever hardware you want, with whatever drives you want, attached whatever way you want (within reason), but just getting the music on the network isn't the hard part of this problem. It's how you want to access it.
Not super related because it's not supported anymore AFAIK, but the original AirPort Extreme (Apple wireless AP) circa 2004 had an audio analogue/digital combo jack on it and you could just go into iTunes and say "play music from that AP" and it would play it. I'm not really an iTunes person but I think if I was the market for that in 2004 it would have blown my mind.
Hope that's remotely helpful... no pun intended.