[rustydoglim]

We have tested these very good value for money subwoofers (<$150) and they worked well with S-1.  One of the model is a downward firing subwoofer, place it on its side so that the driver faces horizontal direction.

Set the crossover freq to > 100Hz.

http://amazon.nuforce-icon.com/category/11753758381/1/Subwoofer.htm