B&W speakers running on Mac 4 ohm taps?

yes, it's safe. I always experiment with the different taps on my Mac. There is nothing bad that can happen from this.

4 ohm taps use additional transformer windings and can often deliver more current.

I have found this to typically be at the expense of upper frequency sparkle and ultimate drive but it is worth a shot.

I am not speaking in regards to Macs, just in general. I almost always use the 8 ohm taps.

I have another question in line with this discussion. With a 6 ohm rated speaker having separate bass and m/t connectors and using a mac amp can one use both 4ohm and 8ohm of the mac in a true bi-wire configuration. Such as hooking the 4ohm to the bass unit of the speaker and the 8ohm tap separately hooked to the m/t unit of the speaker.