Pandora also pays the publishers for the performance right, separately from SoundExchange. This can be a fixed percentage of revenue. Societies like ASCAP, BMI, and SESAC generally administer the rights on behalf of the publishers.
Lastly, Pandora also pays Harry Fox Agency the statutory rate for the mechanical rights. HFA in turn pays the song writers.
Here's a good breakdown from an old and entertaining (view comments) TuneCore blog post: http://blog.tunecore.com/2012/03/the-additional-10-5-spotify...
Check out TuneCore's Music Industry Survival Guide. It's a useful resource.
http://www.tunecore.com/guides/sixrights
Edit: I'm wrong (and so is Tunecore). Parent is partially correct, Pandora does not pay for mechanical rights. They qualify as a PurePlay Webcaster. However, Interactive Streaming services, such as Spotify, do have to pay mechanicals in addition to recording and performance.