HK citation 16 amp driving Magnepan IIa's

The magnepans are labeled 6 ohm but the Citation has only 4 & 8 ohm settings. Which setting would be preferable for driving the Magnepans? Please explain in simple terms as I am not too savvy electronically.
Thanks to all. JB
I had 3 16's and the only settings on the HK 16's as I remember it are for the display LED's.

Where is this "setting" you are referring to?
Tks for the response.

I finally got it through my head that the 4& 8 ohm knob justy controls the sensitivity of the led readout.

Regards, John