Went to the Onkyo site and looked at both the 787 and 797 manuals. My presumption wasn't correct; the 797 has a sub-menu during setup which allows setting 4ohms, but the 787 doesn't have such a setting and apparently has no type of adjustment at all for 4ohm speakers. You'd think that this would imply that there would be no trouble with 4ohm speakers and no adjustment was needed, but that's apparently not the case. The only thing I saw in the 787 manual that might even remotely be helpful was a bass-limiter in the sub-menus. It's unlikely that the bass is being overdriven and drawing too much current, but that was the only thing that was even close.
