You might want to try how I set up the BDP-83 with my 990. The oppo's speaker settings are zero for trim and distance and the speakers are set to large. Finally the sub is set to "on". This should allow the 970 to handle all those chores including bass management. My experience is the volume between the digital optical for DVDs is slightly more than the 7.1 analog output for Blu-ray.
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AvFan
Outlaw 976 | ATI 2005 | M&K 850s Left, Center & Right, Surround-55s, MX-70B Sub | Harmony 950 remote | Panamax 5100 | OPPO UDP-203 | LG OLED55B7