Hi Archtop Eddy,
I hear what you're saying. You want a battery powered subwoofer to work with your Super Octave OC-3. That's it, yes?
And for others, we can swap in some other kind of bass/kick drum type (foot operated) percussion.
The subwoofer has to be big enough, and loud enough to play this kind of instrument (outdoors) and still be as portable as an S1 Pro and run on batteries. It would have to be road-ready and tough enough for portable applications, and still be small and light to be attractive to S1 Pro owners.
That's a tall order for sure.