Audio Children: Future project: NanoBlaster

Since I am unemployed I spend lots of time on important stuff: like designing a portable soundsystem.
I dont want a big and bulky device, so I looked for a small full-range driver with a good efficiency.
Found the Faital: 7 cm diameter 8 ohm 100Hz to 20KHz and 91dB efficiency:

http://www.lautsprechershop.de/pdf/faital/faital_3fe20.pdf
Powered with an Amp-6 from 41Hz that runs on 8 Lithium ion cells (14.4V) and supported by solar cells (1W).
If I power the two drivers in stereo this should give me extremely low distortion @ 2x 13,5W.
I plan to build in a switch that can change the output to mono, in that case I will power the drivers in parallel.
This will give me an impedance of 4 ohm which allows more power 2x 25w (at the cost of lower amplifier efficiency and slightly more distortion)

I plan to build it from 9 mm multiplex and it should weigh about 2 Kg while measuring 22,4*15,3*12 cm.
The drivers are situated next to each other with to bass reflex tube's (18mm) in the middle.
During transport they are protected by a lid that also houses the solarcells, opening the lid will power on the amp. It should run at least 15hr @full power without help from the sun, which could add 15%.
I hope it will be small enough to bring to mountaintops where it should be loud enough to bully Die NKBVAU!!

some alternative designs: