Pc sets aren't really that good
By pc sets you are referring to the z-5500-logitech, gigaworkss750-creative, and the promedia 5.1 by klipsch.
Those pc sets don't come within a mile, or anywhere near quality sound. Its okay for gaming, but I found out that a $80 sennheiser headphone set sounds much better.
If you have to buy one of them., the gigaworks s750 and the klipsch are better in sound, but the logitech's are more reliable.
A note of caution: Some people have reported that their creative and klipsch units break down and that they are a pain to deal with to get it fixed. Reasons cited are high costs, out of warranty charges, not being fixed the first time, example, being charged $200 to fix the gigaworks s750.
Your betting off getting the onkyo set for $400 or better yet the svs, which carries a 3 year warranty and is more reliable by people who KNOW speakers and subwoofers.