Hey Dave .


I put a PinballPro speaker in my Firepower .. cost about $120 delivered around last Xmas .. worth the $$ I reckon.

I think it is this one but not 100% sure .. when I emailed them at the time they recommended what I ended up buying and it was cheaper than the one I originally thought was suitable

http://www.decoratorsupply.com/pinball/Products/Speaker_Products/subwoofers/SP-8/sp-8.htm

Cheers
Dave