I've never fully understood the desire to add more and more speakers and amps to a motorcycle, unless someone just wants to use their bike as a juke box at the gatherings in the parking lots of the world. No matter how many amps and speakers they add, at speed on the highway they will never achieve the same kind of sonic experience they would in an enclosed vehicle or their home. But they can and do irritate the living chit out of others who have to listen to the ear bleeding sound pollution they emit as they ride by us. Kind of like the obnoxious kids who like to cruise neighborhoods showing off their massive amps and speakers, less the extreme bass of course.
If you want truly good sound on a bike, I'd suggest a full face helmet with top quality speakers in it, similar to headphones in overall affect. The downside is not being able to hear what is going on around you, but there again with the regular stereo blasting through six or eight speakers you aren't going to hear that car coming up on you or that fire truck anyway.
JMHO - Jerry