Not to mention I bet I would get a lot better sound out of the receiver/bookshelves, than that of your computer speakers....and what about adding a sub?
Eh, I dunno about "a lot better sound". You're comparing a controlled directivity studio monitor to more typical, flush mount tweeter" hi-fi speakers. I think the JBL's sound really nice, and measure as nicely as any speaker i've seen in the price range:
Their bass extends down to around 45hz as a -3db point, and in most setups I would probably use them with the active bass switch shelving the bass down. If you expect to play them really loud, then maybe the LSR2328 monitors are a worthwhile upgrade, but I can't imagine needing more bass than these high excursion 5" woofersf, in a nearfield computer setup, unless you really want that bottom octave.
A nicer (measuring), but more expensive studio monitor, is the Mackie HR624mk II
http://www.sweetwater.com/store/detail/HR624mk2
Here are its measurements: