I’m sorry, but I’m still not understanding what you’re referring to. MIDI is not a sound engine, and Web MIDI allows for MIDI communication within the browser. ORCA merely sends MIDI messages, which is Gates, Notes, Pitch, etc… Learn-ORCA only produces sound because it includes Enfer.
From learn-ORCA:
For the purposes of this site, we’ve connected some drum racks and synthesizers from Enfer in the bottom right and are patching them in as virtualized midi instruments. Normally, Orca will not make sound on its own, and rather just sends messages or data to external devices or programs.
Incidentally, I plugged my phone into a USB-C hub for monitor, keyboard, and a desktop environment and gave ORCA and Enfer a spin on that. It actually worked great (better than on my Chromebook, actually).