Sound problem: more channels == worse quality

[Richard Shaw]

While diagnosing my sound issues which I at first attributed to my new
Creative T6100 speakers (yeah, they're pretty low end for surround
systems), I found that the sound quality was still poor when I plugged
in my headphones to the front audio port.

Of course after that I started blaming the sound chip (Built in) but
now I'm not so sure. I found that the more channels I setup in
PulseAudio the worse the sound quality.

With 2 channels the sound problem I'm having disappears, just normal
hiss at high volume (amplification). When I up to the 4 channels I can
hear the problem but it's pretty faint and at 6 channels it's very
evident.

The sound itself is a high pitch electronic distortion. There's
probably a technical name for it but I'm not an audio engineer. The
best way I can describe it is that it sounds similar to distortion you
get from very low bitrate audio streams.

So my question is: Is the problem my sound chip (hardware) or
PulseAudio (software)?

My plan is to buy an Asus Xonar DG[1] but I don't have a lot of
disposable income to spend on this problem so I want to be fairly
certain this will fix it.

Thanks,
Richard

[1] http://www.buy.com/prod/asus-xonar-dg-sound-board-cmi8786-pci-24-bit-internal/q/loc/101/217036858.html