The UniSolar Rich mentioned is amourphous silicone. The US-64 has a large area, guessing 2 x 3'.
My Sony MP-3 player uses very little power, runs ~40 hours from a single 'AAA' battery.
The self driven 12V speakers used less 12V battery amps than a lower wattage 9V pair run from a 7809.
The speaker amps vary depending on the sound (or no sound) being produced, and naturally the volume. The ammeter looked like an equalizer bar going up and down with the music. No sound took very little from the battery, 20ma. if I remember right, but the devices surely vary.
Don't series two 12V PVs for 12V use. That would be a waste of panel.
Don't use a blockibg diode with a controller.
I personaly like the Morningstar SG-4 controller for low power use, like 64W or less. Nice & simple, PWM, temp compensation, cheap ($30).
I would expect a 12 to 15AH SLA battery, SG-4, and US-32 PV (if you can find one- they have been discountinued) would give excellent results. Naturally, it would be better if the panel was mounted for a hour or 2 of sun a day, and if the audio devices were shut off at night.
It would be cool to see a couple pictures when it's done.
G-