AvFan,

Have you looked at the Audio and Sound Effect settings on your 980 and they are turned off? I used to own an Oppo 970 that had those features and don't remember if they can affect your hi-rez playback. My speakers are 4 ohms as well and are within 1-2dBs of each other whether I use my Radio Shack meter or the mic that came with the 990. I have the same hi-rez discs you have and many more. Didn't have an issue with either disc when compared to my other hi-rez discs. There may be some perceived differences in the way the recordings were made and may need some fine tuning. Especially so with DVD movies and the center channel for me. But I never experienced a 7dB gain needed in order for a channel(s) to keep up. Only from 1-3dBs. Could also one of the other settings in the 990 be turned on/off as well? Such as Panorama or the Tone Defeat? Just thinking out loud other "potential" issues that may have been overlooked?? Hope you are able to solve this.