Simple explanation that makes common sense.
Lord - R, you really stand by the Marantz name!
Thanks for the info. I really need to research exactly what ohms are as your statement about leaving the switch on 8 ohms seems counterintuitive.
No, I'm an Onkyo guy.

Actually, I'm into Denon, Yamaha, Onkyo, Marantz, Pioneer Elite, Rotel, Lexicon and Anthem.
But I know a good value when I see one.
And these Marantz receivers are it.
*** Receivers that have a two-way swich for speaker impedance, like my Yamaha receiver and yours too, as well your Sony one, are for safety measure to please UL standards about receivers getting too hot with lower speaker's impedance.
But they do that by restricting the power flow from the receiver to your speakers. And by a large amount too. The danger here, is that your receiver will clip earlier that if set to the higher impedance.
Just read some articles and reviews right here at Audioholics about this very subject.
The only and true counterintuitivity is to please the UL standards for power amplifiers, that's it, no more no less.
And a good amp or receiver does not have such a silly switch, isn't now?
Of course, you can always set that silly switch from your receiver(s) to it's lower impedance setting, but you'll loose about half power of your receiver potential.

Is that sounds like a fair compromise just to please the UL Laboratories for power amp standards? I thought so too.
Cheers,
Bob