This is indeed sweet. I haven't done much research on this, so maybe someone else on HN would know, but are there any plans on having embedded "sound fonts"?
This is great! A few bugs: The stems are technically incorrect (from third line up the stem goes down not up) and there aren't natural signs where there should be (G Minor Solo, the D# and D). I assume it's the player's problem and not the XML, if I'm not mistaken.
This is pretty amazing. I can't wait until these audio APIs are out of beta.