Depends on the four Ohm speaker. Simple nominal impedance specs are insufficient to determine the difficulty a speaker will present to an amplifier. You need to know the lowest and highest impedance point and the difficulty the crossover presents in terms of phase angle. The 6100 is a high powered but not extremey high current amplifier. It will be happy with most reasonably well designed speakers.
Nor do I. If it were me, and I had any doubts, I would find information on the impedance and phase angle before I made a large investment in something that doesn't pair well with the amplifier I own. That's what the internet does best, give you obscure information.
I haven't heard the 6100, but in general, Sonus Faber pairs up very well with Mac. I've never heard a bad Sonus Faber/Mac combo. Both are very consistant in their sonic signature.
But as Jan is alluding to, I have no idea how that exact combo will pair up specs-wise.