Well I own the Logiotech 506's and I'm very happy with them. One of the features I really like on the 506's is it has a bass control on the back. They also do a real good job of emulating 5.1 if your source doen't supply it. Nice feature of the analog inputs.
The reviews say they buzz, and they do if you try to connecct up the supplied analog inputs at the same time as the digital inputs. Other than that they were well worth the $100 I spent on them.
Gigabyte 880GA-ud3h / 3.1 Phenom II x2 550 BE Callisto(4 cores and OC to 3.4) / Corsair Vengence 2x4gb DDR3 1600 / 640gb WD Black 2ea./HIS 6870/ 650 EarthWatts / Win 7 64bit