Listening off grid with batteries

Even the MOST efficient speaker is only just over 3% efficient.
Hair Split for the day::
Sensitivity is what you would be after, if you want to go that way.

Atma,
See my post above. Inverters are now being 'distributed' and are at each panel.
In bright sun, you get about 100 watts per square meter (yard?) of area.
The 'where do you put the inverter?' argument harkens back to the early wars between Edison and Tesla/Westinghouse over AC / DC power systems. The advantages of early inversion to AC are huge.
Trouble is, you change BACK to DC to charge batteries, than again BACK to AC this time to distribute to what / where it is needed.
Boats over a certain size tend to have double electrical systems. The DC system of the boat...starting, running lights, communications / navigation and some utilities VS a 2nd 'shore power' system of a regular breaker box and 110 distribution. Boats, especially larger ones, will have a 'genset' which will provide AC and DC for battery charging and 'boat stuff'. The boat people are adamant in opposition to physics in that they measure everything in amps, not watts.

As for off-grid equipment which is more efficient....I would suggest fairly sensitive speakers and a lower power 'd' amp. 'd' amps are most efficient at higher powers, being not much better than a reasonable A/B amp at less than half power. If you are off-grid in a cool or cold climate, some of the inefficiency of tube gear can be recovered as heat for the house and 'defer' those energy costs. A trivial example is my Sony SXRD TV with a 180 watt lamp. This guy kicks out enough heat near enough to my thermostat to make the rest of the house colder....since the darn thermostat thinks it's warm enough.
In the summer, the extra heat causes the A/C to run more........

As for inverters for electronics, make sure they are True Sine Wave. I'd guess all of the low power units used in cigarette lighter plugs are some kind of modified square or triangle wave. I have one in the car for my laptop and to charge my cell phone, being too cheap to buy a car charger, since I already HAD the inverter. I wouldn't trust the sound of a boombox running off that thing.

Don't current solar panels each come with a small inverter? Isn't it easier to move the AC around as opposed to DC? Won't there be less loss this way? You can re-rectifiy it at point of use....for battery charging.
All the listening room needs is a sub panel, right?

How are you handling lightning / surges?

http://ecoustics-cnet.com.com/8301-11128_3-20006619-54.html?tag=mncol;posts

link to microinvertor article