From a purely "numbers" standpoint, the plug and associated switch should decrease output volume by a few dB (roughly 3dB, just enough of a change to be detectable by the human ear) while allowing the sub to go about 6Hz deeper (16Hz instead of 22Hz) - sort of a case of "do you want louder or lower?" Although in the case of the EX, the "lower" mode should still give you rather a lot of volume...