I would say if you wanted to get some Loud speakers, go for the Pioneers, but they aren't going to produce accurate sound (bloated bass they will have).
Pawn shops are worse in larger cities, because the people that own/run them are smarter. The small city pawn shops like the ones in Fort Wayne, IN are kinda stupid and sell things for insanely cheap at times (I got a Kenwood KM-106 power amp for $20 the other day which is just plain stupid, it means the person that hocked it only got $5 for it), and it does require luck and skill (lots of knowledge on the value of things. Quite basically, if you don't know what it is then stay away from it in pawn shops. Chain pawn shops like Cash America allow full refund returns within 7 days and most others will give you a day or two if you ask them politely that if it doesn't work or you don't like it that you be able to return it (most cases they don't care if you like it or not, but if it is broken they will accept a return on some occasions). Most pawn shops also have a 30 day in store credit return policy, but inner city pawn shops are more stingy and you may have to put up a good (pleasant argument) or you may be stuck with it.
That Wal-Mart system is crap with other speakers. It was designed to work optimally with the sub/sat configuration and not really anything else. All the bass is forceably put to the subwoofer (as it should be) and higher frequencies are sent to the satelite (small) speakers. The Pioneers would sound aweful with this system. I would advise getting a stereo receiver from a refurb distributor from Harman Kardon or Onkyo, or maybe a surround sound receiver if you think you will upgrade to surround sound later on.
