My outdoor sound solution is part of a whole house audio system that I am installing on the cheap. Thought I would share in case it gave any ideas.
In total I have 7 zones throughout the house. 6 of the zones use in ceiling dual coil stereo speakers, the seventh is a pair of outdoor speakers. I purchased all speakers, cables from Monoprice or Amazon. To power them I bought a used 12 channel (6 zone) amp and two small class-t stereo amps. Each outdoor speaker I am running in bridged mode to give them a little more oomph. I thought about using Sonos Connects for the sources, but instead I opted for Google's Chromecast Audio devices (at 1/10th the price each). They can be set up individually for each zone and grouped together in any combination with other Chromecasts to play the same source in whatever room you want. All control (volume, speaker selection, source) is done on a smartphone or the PC so yes Wi-Fi is required. I was also able to upload my music collection through Google Play on the PC. So far it is pretty slick. The interface on the phone uses the Google Cast app and whatever app your music is coming from (Google Play, Pandora, Spotify, Tune-In, or any other that is compatible with Chromecast). All said and done I spent about $900 on this project, including all speaker wire and interconnects (the boss gave me a budget of $1k so I think I did pretty good). Next she wants an outdoor theater for movie nights by the pool....wish me luck.