Do this for fun:
MFR Autospawner with an EnderTot., dropping down between several turtles who kill it
2-4 Endermen will spawn, which can be killed by MFR Grinders before the turtles kill them
Profit of 200-400 mob essence plus all the loot.
And yes, because of the way Dart handles the extra spawning they will spawn even on versions that have the "slime essence" fix.
I can't stand the sound. Although, isn't there some sound removing block from Extra Utilities?