Well since you will be using just a single cable, you obviously won't have true 5.1 surround but thanks to the built-in decoders they can convert that 2 channel signal into a 5.1 signal with very good results.
The surround effects include
-6 channel direct
this is true unaltered 5.1 surround which you can get through the triple 3.5mm jacks.
-Stereo
This just turns any signal into 2 channel stereo (only uses the left-front and right-front speakers)
-Stereo x2
Same as stereo but includes the rear-left and rear-right speakers too
-Dolby ProLogic 2 Movie
Optimized Prologic decoder for movies, vocals are tuned more to the center speakers while background music is spaced among the surround speakers
-Dolby ProLogic 2 Music
Optimized Prologic decoder for music. It spaces the sound out among all the speakers in a way that makes music sound better. This is also a great setting for games.
I love my Z5500s, the speakers use actual speaker wire (good if you want to get thicker cables). The 10" subwoofer is very high quality, it can take a lot of abuse from even the most bass-heavy music without distortion. Each of the satellite speakers have bases that rotate around so you can mount them onto the wall. It is kindof a pain to mount them but it is worth it. I haven't heard the Z2300s but being that it is a Logitech product, it is probably very high quality. Both have decent sized subwoofers for good bass reproduction. If you have the money, go for the Z5500s because surround sound just sounds great no matter what you listen to.
