This brings back good memories. It really was the defacto media player for me, for so many years. I couldn't figure out what else this does other than play, pauses, stops and changes volume? How close to fully functional could this go? Can you adjust balance for example using the HTML5 audio API?
I originally thought it was impossible, but today I found this Web Audio API doc, and I think it may actually be possible not only to do the balance, but also the equalizer. I'll at least look into it more.