the klipsch promedia has good build quality and sound is not bad however the satelites are far too underpowered for the subwoofer included and the subwoofer even on low levels completely drowns out the satelites.
the logitech z623 while not best in show sound quality is certainly not bad and is a decent choice.
i dont know much about the z2300.
you should take a look at the jbl creature iii and harmon kardon soundsticks iii as they are also excellent speaker systems. sound quality is likely going to be better than the logitech set however the logitechs are known to have more powerful subwoofers so will be more boomy with the bass and may be louder in general.
however perhaps the best sounding option for your budget would be to get a pair of bookshelf speakers and an amplifier cnet has a $70 mini hifi system guide which uses dayton speakers and a lepai 2020 amp you may want to look into. since you have a larger budget you could go with a nicer amplifier and perhaps different speakers. home theater/hifi speakers completely blow pc speakers out of the water in many cases.