Quick question: would you be able to get a cheap AV receiver to use? Almost anything could work as long as it has S/P-DIF/analog inputs and an LFE output, e.g. anything from the last 15 years. Maybe you know a buddy who's upgrading, or perhaps there's a garage sale down the street? Having something like that would greatly increase your options.
Assuming that you CAN get something like that, I would strongly recommend something like this:
http://www.amazon.com/Behringer-B203.../dp/B000LQ2ABK
This is the passive version, since the active version costs a lot more. If you have the receiver then that can supply power anyway, and the LFE channel opens up the possibility of adding sub(s) later as necessary. The 8" woofer gives a pretty decent low-end; I've run it down to about 40 Hz full-scale and it seems to be OK for most types of music. Would be worlds better than what you have now anyway.
See below for more info:
http://www.zaphaudio.com/blog.html (search for "B2031P")
http://dtmblabber.blogspot.ca/2010_07_01_archive.html
The KRK Rokit 6 is not much more in terms of $$ and is likely to be similar in terms of SQ but it doesn't produce as much bass due to its smaller woofer.