I have had some time with Onkyo and these are some of the things that can immediatley fix low sound problems with Onkyo, trust me I have spent lot of time on reading-testing-re-reading-fixing. If you are configured correctly then at 30-40(already high) level should be perfect for a normal room to listen, if you have to setup your system to >40 it means your speakers / configuration needs some tuning,
unless you want your neighbors to call police or its intentional for large party
Before you make any changes, ensure to change the mode to ALL channel and then test again.
a) Upgrade to latest firmware and then do hard reset (procedure available online easily).
After running Audessy EQ, save , restart and proceed as follows -
1) Enable Dynamic volume - from OFF to LIGHT.
2) Increase intellivoume - from 0 to 5 (atleast) can be done upto 12 , 5 is a good starting point.
3) Enable panorama to ON
4) Enable Music optimizer - ON
Additional settings as below -
If you are still not satisfied , please try additional settings -
1) Goto speaker setup and ensure that no specific settings is higher (negative) , this dilutes the power output, example : Audessy EQ might set it to (-8) or (-9) in such a case a lot of power of even high end speakers can be diluted.
Try to change the value in + example if you change -8 to -1 or +2 you will see significant improvement immediately.
2) On top of it, if you have done OFFSET setting to -10 or - 15 or -20 trust me, you will end up believing onkyo is not good or defective , best is leave off-set to 0 (default).
Onkyo receivers are the best all rounders after a lof of what I have tried for home users.
(high end other brands >10K USD excluded).
The above suggestions will surely make it amazing improvement, feel free to ask me in case of any doubts.
Happy to help as much as I can.