There's also a particle system effect when you play a sound, I say make it exactly like the real deal. If Valve gets upset, they can always make those sounds unplayable.
Couple things, admin/cooldown would be nice, plus why don't you precache all the files at once and then look at the menu_item index to determine which one to play. You'd save some unnecessary string conversions. Other than that, good job, I knew someone would make something like this.