I have RealTek HD ALC662 on my mobo and it is just my opinion they supply a low quality software driver. I originally tried (non amped) PC speakers. Everything maxed sounds like people whispering. So for the last year, I ran the line up to my stereo AUX and boosted the volume through the stereo.
Without resorting to external amps, alternate sound cards and other cheats. Your only hope is to run a sound manager in the background, with a graphic eq. cranked. Even then you are still going to be very soft volume.
Until someone kicks the programmers in the butt at RealTek to create a better driver, your solutions are very limited on this one. I haven't found any 3rd party help with this either and like I said, the better part of a year.