Mixing 4 and 8 ohm speakers

SiddPolk
SiddPolk Posts: 8
Tweeter out my way is closing their stores, and offering fantastic deals on Polks, so I picked up a pair of RTiA5s, RTi8s (from somewhere else), a single RTiA3 and an LSiC. Didn't realize the LSiC is 4 ohms until I got it home. For power I'm using an Onkyo 805 and Parasound 2250. With the speaker ohm issue, I'm currently bi-amping the RTiA5 fronts with the onk, driving the rear RTi8s with the onk, and routing the center through the Parasound right channel to the LSiC.

So I've got a couple of questions.
1. The Onkyo has a setting for 4 ohm and 6 ohm. If memory serves, you're supposed to have it set on 6 ohm for 8 ohm speakers ... so it doesn't sound like a good thing for the onk to mix in a 4 ohm. Anybody know about this?
2. I didn't want to bridge mono the Parasound for the LSiC, too much wattage and kids in the house. So I'm running a normal stereo setting, but only using the right channel. Will this cause a problem with the Parasound?
3. Any ideas I'm all ears.