^ If I understand you correctly, you have HDMI 1 from the OPPO going direct to the Display for video and HDMI 2 from the OPPO going to the AVR for audio.
Is audio "Late" -- lips move before you hear the sound? If so, you are probably suffering from the "helpful AVR" problem. Your AVR doesn't know it has been bypassed for video and so it is applying a chunk of audio delay "to be helpful" -- i.e., to compensate for its own, internal video processing time.
To fix this, you need to convince the AVR it isn't processing video. Either disable its HDMI output or set the AVR to "pass through" for HDMI video.
Audio and video are in sync at the outputs of the OPPO (with the A/V Sync setting at 0). If you can't figure out how to get the AVR to stop altering the audio timing then you have two choices. First, run video through the AVR as well. This is the normal way to wire things, and you'd only avoid it if your older AVR can't handle the type of video you want to send to the Display -- e.g., 3D video.
Second, get a calibration disc and use that to adjust the A/V Sync setting. Using a movie disc to try to adjust sync is a bad idea because movies usually have inherent sync error, and that can vary scene by scene. If you adjust things properly with the calibration disc, the inherent error in movies will likely be too small to notice.
The sync chart I recommend is on Disney's "WOW World of Wonder", Blu-ray, calibration disc. When using it, sneak up on the correct A/V Sync setting from both sides (audio set too early and audio set too late) until you get the hang of reading the result consistently.