I’ve been trying to play more than one sound simultaneously in the iPad browser, and it appears that it isn’t possible using raw <audio> tags. Starting one <audio> source will always pause any other playing <audio> sources, whether they were initiated via user tap on the controls, or with the .play() method.
Are there any other approaches that might work for multiple simultaneous sounds (QuickTime, <embed>, etc.)?
Now that iOS 6 is available, WebAudio is the way to go. This is still not possible in iOS 5.