Sonos is a nice, affordable and easy to implement music system. If at all possible I would visit a local Sonos dealer and ask for some product demos with some outdoor speakers, and I would do this for two reasons:
1. Sound quality, make sure the speakers sonically meet your expectations.
2. compatibility. Outdoor audio zones can be tough on an audio system to play to the levels that homeowners want. Because there are no walls sound pressure levels (volume) drops off quickly the farther away from the speakers you get. Because of this I recommend speakers that are efficient and easy to drive. When using the term easy to drive I am referring to the speaker’s rated impedance rating. Try to look for a speaker that has a rating of 8 ohms. This indicates the speaker will be much easier for the amplifier to effectively drive (this is important for digital amplifiers like those used by Sonos).
The other number to look at is efficiency and this number tells you how effectively a speaker converts power into sound. The higher the number the more efficient the speaker is (this means it will play louder).
With these factors in mind try looking at products from Boston Acoustics, Terra Loudspeakers, Sonance, Niles Audio and Monitor Audio. All of these companies offer speakers that are considered efficient and easy to drive, and they have good reputations for sound quality. Niles and Sonance also offer a vast selection of rock speakers, planter style speakers and traditional outdoor speakers so you’ll have lots of choices.