onkyo 804

Anyone have any problems with the unit going into protection mode when running 4 ohm speakers in the front? About to purchase and want to make sure all will be well. The rear surrounds and center are only 8 ohms. Its just the 2 mains that are 4 ohm. Any help would be great. Would the harman 645 do a better job in this situation? I kind of wanted to stay away from harman due to bad experiances with reliabilty in the past. Thanks for the input.