Ok. I suspect my Oppo issue is loser error on my part (it seems that the RS meter doesn't go below -10 on its dial!) and I bet that Oppo + Discrete will turn out to be -15dB.
In other words, the Oppo 980 is applying the -5dB adjustment on its analogue sub output even when the main five speakers are set to "Large". A bit annoying, but I'll be happy if that is the explanation.
Hopefully, many of us will be using HDMI soon. However, I suspect that the Oppo will also apply a -5dB offset to the LPCM sub channel.
This -5dB offset is going to be player dependent and is something for everyone to watch out for!!!