I have the Pioneer VSX-819, and it has a similar feature called midnight mode. I haven't used it because I only have a two speaker setup (i think it only works for surround sound), but it processes the audio so that even at low levels you can hear a greater sound range and not wake up the whole house. In any case, this should level the playing field between the Pioneer and Onkyo in this regard.
Personally I am loving my Pioneer, however I cannot speak for how it compares to the Onkyo (or any other receiver for that matter). I feel like it gives my speakers plenty of power.
Comparing the two, my thinking is that since they are approximately the same price they are probably very similar in power and SQ. I would be surprised if there were an audible difference in a blind test, but of course I do not have audiophile ears. If you are unable to do a listening test with both, then it might just come down to which brand you prefer.
I hope this is helpful.
Good Luck!