I always got not-so-great sound from onboard audio, probably from being so close to fans/graphics card/power supply.

Also I couldn't control volume directly.

What I have found works great is an offboard dac:

    https://www.schiit.com

Just wire it up using usb or toslink/spdif to get digital sound to the dac cleanly, then the dac is isolated from everything and you get a volume control.

I use headphones + mic + fulla (soon gunnr) but this also works for straight headphones or speakers with other models of dac.