I went to best buy, circuit city, and compusa and listened to just about every speaker there is last week.
The logitech z2300 are amazing for being 2.1.
The logitech 5300e are amazing too as well the 5500.
I'm guessing there is a difference, but honestly I didn't notice a ton of difference in sound quality between the z2300 and z5300e when standing up close to them just listening to music. When you hooked them up to a tv/home theater system though, the 5300 and 5500 were surely better for that application. The 2300's though are more than adequate for an awesome pair of desktop speakers for a laptop. They will blow you away.
All three of these systems are definetly THX speakers. They have a very movie theater like sound to them. They sound pretty dang good with music, but some have complained they lack midtone. They surely have the roar and punch you'll want for games and movies though.
If you don't like that movie/gaming sound and want something w/ a very very clean stereo speaker sound the klipsch 2.1 setup may be better for you.
Best thing you can do though is go check them out. You will be suprised. Some of the speakers you think look good will actually suck, and some of the speaker you think look like they will suck actually sound awesome. I almost made the mistake of buying the creative I-trigue speakers and then the JBL creatures. Both of those sucked when next to the logitech and klipsch. I actually decided to skip all of them though and just hook the laptop up to my stereo system which has sound probably comparable to the klipsch 2.1, which is good enough for me right now. The stereo speakers I have now (awia brand) have built in subwoofers and make my room bounce as it is.
The harman/kordan sounsticks have pretty dang good sound to, but I think they are hideous. The klipsch 2.1 are not very pretty either. And by not pretty I mean, not desk pretty, ie. eye sore. The logitech look nice and sound nice. Win, win.