FWIW, You've chosen the right tap when you get the sound you enjoy most. Since you have speakers with a nominal 4ohm impedence I'd start with the 4 ohm tap. If your speakers don't have a serious dip in their impedence in the bass you will probably get the best match off the 4 ohm tap. But, if the speaker does have a serious dip in the bass your sound may become enimic and may benefit from using the 2 ohm tap.
Anyway, its likely that there is not perfect fit in any evnt, so just choose what sounds best to you. You won't damage anything.
Anyway, its likely that there is not perfect fit in any evnt, so just choose what sounds best to you. You won't damage anything.