I have a pair of Z560's, and I would seriously doubt that the new speakers that replaced them are louder/sound better with half the power. With a good sound card my speakers sound great.
5.1 is great, but most people seriously don't
need it.
Although, I'm thinking of upgrading my speakers to the Z680's.
http://www.newegg.com/app/ViewProduc...121-105&depa=0
I've compared them to the Klipsch ProMedia 5.1's, and I just like the Logitech speakers better. Although, It all depends on how you like your music to sound, but you can't go wrong with either one. Plus, I have a ton of Logitech products, and love them all.