This is exactly where jsmad could shine, even on current browsers (on FF4/Chrome10+). Game usually use small sound effects, that can be decoded in a few ms and then stored in buffers. From there, it'd be very easy to do the mixing in pure JS using audiolib.js - which is a treat, btw! You'd get as many audio channels as your CPU can handle, mixed in realtime. If the Audio Data API / Web Audio API support more than 2 channels, we might even be looking at full 5.1 demos real soon.

This is so exciting!