http://www.engadget.com/2010/09/10/logitech-z506-review/
The feeling of immersion in Hero's guqin courtyard fight scene was fantastic, with raindrops hitting the pavement all around, and we felt every bullet whiz by during Neo's infamous bullet dodge in The Matrix thanks to punchy front and rear sound. Solitary singers came through high and clear in the front and center channels, their words reverberating off the auditorium walls behind us, while orchestral pieces and applause shared the front but with a welcome rear bias. Tossing flaming barrels with our Half-Life 2 gravity gun, than quickly turning away, we could easily tell by audio alone in which direction they'd exploded, and the worlds of Mass Effect 2 took on an incredible sense of immediacy with futuristic advertisements and alien conversations bombarding our ears from all directions at once. In other words: surround sound kicks ass, and these speakers are excellent boots.

Wrap Up
If you've never experienced true 5.1 surround sound, have a capable sound card and your content primarily resides on your PC, the $100 Logitech Z506 are a fantastic introduction, but we can't honestly recommend them over the company's far-more flexible X-540 set -- the obvious choice at the $90 you can presently find them for. When it comes to analog surround sound, anyone can hook up two or three sets of quality two-channel speakers to get a similar effect, so the onus is on Logitech to make combo 5.1 packages like this easy to use and set up. We're mystified why the firm would ever introduce a package with less bang for the buck.

http://www.expertreviews.co.uk/pc-speakers...8/logitech-zAll
All of our test tracks sounded excellent through the Z506 set; acoustic songs were suitably mellow but with crisp detail, even at low volume. Turning it up for our heavier songs, the speakers comfortably filled our test room with sound. Both rock and electronic music had plenty of bass, but the satellites could still be heard clearly over the subwoofer. Once we’d fine-tuned the bass, movies also sounded fantastic. The surround sound effect in Casino Royale’s opening chase scene was very convincing, with each speaker picking out finer details as well as all the major action.

Although it isn’t without its faults, we were still impressed with the Z506 set and its superb audio quality. It costs slightly more than the older X-530, but it has a greatly improved design and everything we played on it sounded fantastic. You’ll need to spend a lot more to get a better set of 5.1 speakers