First, you will not get bass back to the rider.
For the speakers pointing back, use an 8 inch Pro Audio driver. You can use 10's also, but they will need more power and are also heavier. Look under the link pro sound then look to right for the drivers at www.partsexpress.com
Consider using the coax ones which allow the HLCD to screw into them. You should also run a search here using the term tower speaker or read the pro audio posts on diytower. I am using 4 pro audio speakers of which two are the coax style with HLCD inside. It can be heard way past the rider. If your amp will bridge mono use that and use the 160x2 amp for that set of speakers. You will not need the 4's.
(Message edited by sea_ray_dave on January 09, 2007)