Bingo.
Mega/Gigaworks series are not comparable with the Inspire. I'd know, my flatmate had them. Prior my purchase of the Giga I also compared them to the at-the-time flagship of the Logitech (Z-680).. which costed more than the Giga at the time, but depreciated a lot it seems. Certainly between those two, I find the Giga to be the more well-rounded speakers. The Logitech was definitely the one with more "boom" to it, which I thought worked for Games/DVDs, but I disagree that they are better for music (unless that is the sound you look for of course). I can't comment on the Z-5500 having not heard them, but I find interesting that some reviews consider them better for music than the Gigaworks. They -might- be (I wouldn't know), but on the technical side, they still lack tweeters, one of the thing that makes the Giga good on the upper side of the spectrum. The sub, while not as big as the Klipsh/Logitech flagship offering is still quality and quite capable of annoying the people living in the same building. Some of the folks at 3dss who've heard it both seem to assert that the Z-5500 has improved on the subs of the Z-680 (giving me the impression that Logitech aim their product more to those who give priority to bass - which is not a niche market).. although the Giga is still considered the better all-rounder.
That said, I think it is fair to say/expect that the Creative Gigaworks, Klipsh Ultra and Logitech Z-5500 would all make mince meat out of lesser multimedia speakers (i.e. Inspire) in any case.