Step 2: The parts.
Altec Lansing BXR1120 2.5 music and gaming speaker. It was originally powered by a 9 volt ac wall wart. I first tried powering it with a 5 volt dc USB Battery pack but the sound was noticeably distorted over the wall wart especially as the volume was raised. I then went to RadioShack and bought a 8 cell aa battery holder for $3. This gave me a little over 10 volts dc with rechargeable cells at 1.2 volts each. This seemed to match the sound of the original setup.
I also wanted to have bluetooth wireless capability I found a cheap unit on Amazon that looked like what I was after. The Enerpak Tube 5000 mAh external battery pack was from living social but these things are everywhere now days. I actually have a smaller battery pack that I was planning on using if it last long enough for a bike ride.
I had found a good deal on some saddle bags over Christmas not realizing they would stick up above the rack surface. This seemed to work to my advantage though as these speakers seemed to nestle in between them.