Not connected
The dial shows volume level as a ring position based on "max volume", since MusicCast doesn't expose the real range without a status read. Adjust it to match your speaker if it looks off — the +/− buttons work regardless, or use Discover to read the real max/step from system/getFeatures.
"AUX" is a best guess — Yamaha's input IDs vary by model (aux, aux1, line_in, audio1…). Use Discover if your browser can read the response, or try a custom ID.
Talks directly to your speaker's built-in MusicCast API over plain HTTP on your local network. Browsers can block reading the response from another device (CORS) — commands still work, they're just "fire and forget" with no readback, and now-playing info / album art will only appear if your browser allows that read. Nothing here ever leaves your network.