The External Audio Effect allows you to specify speakers and you can use any number of these.
How would you do that? As far as I see, I can only create a row of effects, with the returns going back into the same track after the External Effect device. This could work for live input (be choosing the original input as return), but would not work for synthesized sounds or tracks, unless I patch a hardware cable to reroute my sounds...
I put eight parallel externals into a rack, and map the gain to the eight macro knobs, automating these from my panning device. I then place one instance of this rack into each track that will go to the speakers. You are correct, the signal chain stops with these devices - they are the last device in each track's chain.
Not perfect, but better than a poke in the eye. You can accomplish a variety of routing solutions, and you can also write reasonable spatialization code.