NEED HELP

Idea: Find a boombox which can take a DC voltage from an external source. Rig up a DC-DC converter that matches your pack voltage and the voltage the boombox requires. Put the DC-DC inside the fairing on the scooter, and rig up a mounting that lets you easily detach the boombox. Then when you park you can easily unplug the boombox, unhitch it from the scooter, and carry it with you.

You may be able to use the stock power adapter.

I've checked this for myself - The typical power brick is rated for 120-240 volts AC on input, however it turns out many can convert a DC input voltage to the desired DC output voltage. Meaning you could plausibly use the stock power adapter which comes with the boombox, connect it to the battery pack, and be good to go.

Hi there. Here is what my stereo install looks like.

http://visforvoltage.org/forum/5197-xb-700-li-mods

Some of the pictures seem to have disappeared but you can get the idea with whats left. I just found this setup on Ebay.

http://cgi.ebay.com/ebaymotors/Motorcycle-Scooter-Speakers-Amp-Radio-Stereo-Audio-MP3_W0QQcmdZViewItemQQ_trkparmsZ72Q3a1171Q7c66...

The speakers are same as I have but the amp/radio is a little different but you should be able to figure it out. Also you should surf Ebay and look up motorcycle stereo systems and see what you can find.
Good luck. Lovin my tunes, Scott.