Sounds about right with some onboard audio. My Z77 mpower has a different audio chip but I had the same issues, it was just never loud enough. I tried all the stuff you find online but nothing made any difference, and I used the green port. I bought a Soundblaster Z and now I can make it so loud it would probably make my headphones explode.
Solution: buy an external DAC and headphone amp, or buy a sound card with headphone amp if you aren't a complete audio snob.