I use a 5.1 system, so the other outputs/inputs are already being used. Also, drivers let you change them the way you want...

I use a Gigabyte Motherboard with a 889 Realtek onboard chip. Not bad, but I had a problem when I plugged my cans (Sennheiser HD 438) in the blue output, there was no bass at all! Problem was solved when I used the black output. Did you already tried using another output?

Just use the rear output.