with any recent solid state amp there is no setting necessary to make the amp work with different speaker impedances. It's a different deal with tubes. The recent receivers that have a switch for 4 ohm operation aren't using it to improve performance. In fact it degrades performance (limits available power) in order to meet government requirements regarding heat, etc. developed when running hard. I would not run a bunch of 4 ohm speakers on a receiver that is not specified to be able to handle 4 ohms, because solid state amps have gerater problems (heat, mostly) when driving lower impedance speakers. (Tube amps are just the opposite, BTW). But that's not what you're talking about.
In short, especially if you don't intend to listen painfully loud, your potential issues are more about ability to provide enough power to each channel without running into undesirable (ie audible) distortion. And that's a real can o worms, becuase while almost no receiver can put full power ointo five or 7 cnhannels simultaneously, they also are never called upon to do so except on a test bench. If, for example, the surrounds are audibly "one notch" quieter than the fronts (3 dB) they are using one half the power the fronts require. Everythings's constantly slideing on a constantly sliding scale. I havent' gone looking for receiver reviews with power tests in a while, but they exist. If you're worried, look at them and get a feel for what seems to do teh best within your price range.
I will say that as a VERY broad generality, it seems to me that Denon, Onkyo, Pioneer and Yamaha are roughly comparable at roughtly comparable price points in terms of all channel driven power and (to a lesser and less-well-known extent) ability with truly low (4 ohms or lower) speaker impedances.