Don't use nearfield studio monitors like KRKs!! It's not that they won't work - I actually DJ'd my first party with KRK RP8 and they worked fine (luckily). It's just that they aren't meant for that and can be easily damaged if you use them at party volumes over and over. You want a powered PA speaker (you even said yourself "PA system"), look into brands like Mackie, Behringer, Electro-Voice. I pulled this image from a guide on suitable speakers for DJing. I own a pair of the EV ZLX-12P and a sub myself. It's a dream setup, I haven't yet played a gig that they haven't kept up with ( about 200 ppl max is what I DJ'd in front of).