Unfortunately "ground" is a very misunderstood and misused word. In this case, we want to prevent leakage and other noise currents from using our audio ground wire to return to their source.
If your circuits use Romex® (NM) or individual wires in a plastic conduit and your walls have wood framing, then you don't need additional ground wires as your ground is already isolated from those bad random currents.
In the real world, ground is seldom ground no matter how much we or the schematic want it to be.