you do not want the klipsch promedia.
i had a pair for a few days and returned them. the subwoofer is much too large for the speakers and unless you turn it down all the way it completely overpowers the satelites which are on the weaker side. sound quality is pretty decent though as is build quality which is why even when i returned them i bought klipsch satelite speakers and subwoofer (quintet iv) and have been very happy with them.
as far as audioengines are concerned,
while they are not bad speakers for a 2.0 they are very picky about placement. place them too close or too far from a wall or at the wrong elevation and they can sound like complete crap. place them well and they can sound pretty decent. i do think that the price on them is way too high for what you get though. decent speakers if you are okay about placement and price
i dont know a whole lot about the swans,
but what i have heard has certainly been positive. keep in mind that they arent big theater speakers and have relatively low output power. i've heard that you will want to keep the mini subwoofer on your desk as well.
what are good speakers for cheap if you wanted a stereo setup,
micca mb42, pioneer bs22, dayton b652 (at least they were.. its hard to know if they still are). klipsch kb-15 icons are good if you like brighter treble. monoprice makes some nice budget subwoofers
as for full 5.1 systems... you might be happy with that speaker set listed earlier and receiver but hard to say... never used that speaker set myself but the brand is decent.