I also try the Netflix Add-on to check for temps, but I cannot find a way to select a fullHD stream, it stays at 960p max.
As for spotifyd, it just works !
I’m using the port from @jant90 available here : Release: Spotifyd addon for CoreELEC
I’m not sure about the dac stuff. I used the headphones jack located on the dac board, but the sound seems saturated 
On the other hand, the RCA outputs deliver a good sound 