It may be just me, but Apple's website seems to beat around the bush regarding the use of Airplay. I just need to know: Over wireless can I stream directly from my iPhone to an Airplay-Enabled 3rd party sound system (No AppleTV, no Airport Express, no Macbook)?
Yep. Apple licenses the receiver portion of AirPlay to 3rd party manufacturers, so they can build compatible receivers meant to work with iOS and OS X devices.
As long as the device you're going to use is AirPlay compatible, it should work.