tamprim

I'm very new to HT, in fact i just bought an enrty level HT reciver, a Sony 845. I've got a question on my setup. I have KG 3.2 mains a SC1 center and some sonace in ceilings that i was going to use as my surounds. The in-ceilings were left behind by the previous home owner. I pulled down one on the sonance and it is rated at 6 ohms. While the others are 8 ohm. My reciver has a 4/8 ohm selection. Should I set the reciever to 4 or 8? Thanks for any help. Todd