Playing random sounds: have you tried 'Play sound by name'? E.g. play sound:
"player" & floor(random(5))
will play one of player0, player1, player2, player3 or player4 randomly. No need for extra events.
About the tag system: what would you propose instead? Previously Classic had a 'channels' system where you play a sound on say channel 5, then you could modify channel 5's parameters. However, some people found that confusing or limiting as well since you can only play one sound on one channel so there's no grouping. With the tag system if you play all gunfire sounds with the tag "gun", you can manipulate all the currently playing gun sounds at once using the tag "gun", whereas using the channel system it's extremely difficult to do that. So do you have any ideas what would be better than the tag system or how it could be improved?
As for muting, which browser are you using? Different browsers have different levels of audio implementation at the moment, for example Firefox until very recently (FF11) didn't support looping. So maybe try different browsers and see if it works better. There's not much we can do about that, the browsers have audio limitations, and you'll run in to them in HTML5 regardless of what tool you're using. We've done our best to work around some of the browser limitations but unfortunately there's still some trial and error involved.