I know this is an old topic but i thought i'd add my bit.
I used to have a logitech z2300 that my dad bought me for a christmas years ago. When setting up a system for my friends, i'd get em a z5300 which was very great, good sound and nice enough.
Sometime around when i got my 360, i upgraded to the logitech z5400. I LOVE it! Got it for AU$250 which is awesome, and it is one of the best small systems i have EVER heard. It has 1 6ch input (or 3 seperate stereos), 2 optical and a component. Oh, and a wireless remote unlike the cheaper models. I have read in this thread that music sounds bad from home theatre setups, but obviously mine is differently. I absolutely love the way it sounds out of this system. It can be cranked so loud, and it will remain clear. This system is a huge step up from logitechs crappy x 5.1 series. The system is awesome for gaming. I run the optical from the 360 and have dolby digital. I run the PC just into the stereo input and have it running on dolby plII music (the best preset).
Watching transformers on HD-DVD, with this thing cranked, the noise at 1 hour 56 mins in shakes the house. Like hwne i have it maybe 3/4 of the way up the whole way through, things are vibrating in my room and it sounds perfect. When the specific scene hits, this up the other end of the house are vibrating. I can seriously compare the setup in my room to the cinema, just obviously on a smaller scale. Im using a 40" samsung lcd.
Anyway, thats my input. This system rocks, but much to my disappointment, logitech has discontinued it, as they did with the 5300. I sent em a complaint email cos this is the perfect system. Now its a crappy 1 input wired remote gaming system (the g51) or the all out 5500.
Anyway, it rocks!