Leave it set to 8ohm. It should be fine. Just watch long periods of jamming. If it does not go into protection mode, just note the level, and try not to jam that loud again. An external amp would be a great idea now or down the road. I have a Yamaha 1400 with 5-channels all 4ohm. The receiver never shut down over a period of about three months. Then, wanting more detail, I added a Adcom 5-channel amp and now use my 1400 as a pre-pro. It will blow you away. BUT, it was fine running the system on it's on.