To each their own, and I wish you luck with the project but it sounds like a bad idea. I have a decent sound system in my convertible, but it still does not sound great once you get some decent wind noise going above 65mph. It is going to be far worse on a scooter. I can only imagine where you start cutting to put speakers, unless you want to install forward firing speakers in a top box, six inchers are going to be tough to find a place to put them. And a subwoofer firing into your butt from below the seat just is not for everybody.
Then there is the issue of messing with a scooter's electrical system for the demand.
At best, you can listen to some tunes over the exhaust, motor and wind noise up to about 40 mph. At worst you have spent a lot of money to fry your electrical system and render the scooter into a nice big paperweight. And neither is really going to impress the ladies.
But yeah, good luck.
