Why not a boom box? You HAVE power out there. But if you want a permanent system, then you'll need outdoor speakers.

You can get everything from cheapies at $50/pair on up to TechNomads for $750 a side--or even more! There's nothing better--cruise ships and the New York Shakespeare Festival's Shakespeare in The Park use Technomads for their outdoor audio.

Boston Acoustics, Niles and others make excellent outdoor speakers (I'm partial to Bostons, but don't like their electronics). Pricing is about what good indoor speakers cost.

I think Bose is terribly overpriced for the quality of the speakers and their sound.

You'll have to run waterproof boxes and underground conduit back to your house, but it doesn't have to be code for speaker wire--I'm assuming you want to keep the equipment inside.

Very little electronics is designed to live outdoors, thus the running of speaker wire back to the house. Some is water and humidity resistant, but that's going to be lousy or expensive.

Or you can find the biggest, loudest boom-box, the kind with removable speakers and just plug that in, and drag it inside when it rains.