if you want a small pair of active speakers, I recommend the Micca PB42X
instead of the audioengine.
If you think 15W is kinda low (for computer sound, not necessarily but I don't know how loud you want to go), get the passive version
with a 50W tripath amp
I use these with a small $25 20W amp
and they sound really good (that's the setup I use with my turntables) The sound is not flat because fuck that, we're no sound engineer. It's warm and colored and with the right amp you can get a decent amount of bass.
Price of the whole setup: $100** /$140 depending on the amp you want to get. Adding a subwoofer to that setup is another story and while it's possible with a 2ch amp if the sub has a proper crossover, it'd probably better getting a 3ch amp.
** the passive speakers + a better amp is cheaper than the active pair listed above, go figure