I agree 2D shooters are silly if you are a serious person !, thanks for the -1.
Question ? : How many enemys do you have in screen ?, you might not have encountered this yet!
And suppose you explode all enemys at once ?, do you also play those sounds individual ?, i bet your speakers explode to ( especially with 64 or 128 channels playing at once )!
Now you have a -1 back from me, greetings.
Tip : dont drink alcohol, its bad for you.
I'm not sure why you think it's a "serious problem." It's not. Have you played a game where there are multiple people firing a gun at once? I'm sure you have. How did they solve this "serious problem"?
If you are concerned about playing too many sounds at once, you can of course limit the amount of simultaneous sounds you play in your sound engine easily. Whether 2 enemies or 100 enemies explode at the same time, you can limit the number of explosion sounds playing at once so your speakers don't "blow up to" (Let me add, playing 128 channels at once won't cause your speakers to blow up, it has nothing to do with it. it's the amplitude of the sounds coming out of the speakers that would cause them to "low up" not the number of mixed sounds signals coming out of the speaker at once).
Changing your game so enemies can only all fire at the same time is a terrible idea. You must agree with that. That kinda of shoot'em up would suck so bad. I'm sure the OP doesn't want to make that kind of game.
I'm sorry you got upset about having a -1, but think before posting, if what you are suggesting would make a game terrible, there's a chance you'll get a -1.
Good luck.
P.S., drinking alcohol is fine, just don't make it a habit.