As Stanwal said, it depends on your speakers. I use the 4 ohm tap with my Magnepans, and the 8 ohm taps with my Spendors. I suggest looking at test reports of your speakers, and see what the impedances are at the most current hungry frequencies (bass) and use those taps. Stereophile is good for this info if they have reviewed your speakers. It is really just a matter of optimum power delivery.
