IMO If you have anything with an optical output (Mac, Xbox360, PS3) then get the Z-5500s, you really won't regret it. There may be monitors out there for the same price that beat them for music, but give it a digital 5.1 input and the Logitechs will really blow you away.
Plus, if you have a house party, the Z-5500's will NOT let you down 😉 I've only ever turned them up about 3/4 of the volume and they are deafening! I've had them about 18 months now, and I must say they are one of the purchases I don't have ANY regrets about (although I'm sure my neighbours would say otherwise) 🙂
Ed