After getting my hellfire in I decided to add another speaker to it although I didn't have extra money to spend on a foxpro rebranded toa speaker. Here's how I did it:
Take a toa speaker or any other kind with a positive and negative wiring to it.
Solder a 3.5mm stereo jack to it (has to be stereo to work with foxpro)
Install heat shrink tape if desired and attach speaker to foxpro
Enjoy
If you have any questions please ask pics to follow