Monitors & Soundcard Help

[arachnd]

I've been practicing DJing and Production with a 3 year old version of these: http://www.logitech.com/en-us/speakers_ ... evices/231
Things sound good but I think I can get a crisper sound out of some real monitors.
So I was wondering if anyone could recommend me a pair of nice monitors? I suppose I'd have to buy a soundcard as well, so if you can suggest something that would be great!
I'm happy with spending at least $400 for the monitors (I was thinking about the KRK rokit 6? - I heard they're pretty good bang for buck). I'd feel happy to spend a grand for everything but if I can spend less that'd be great.
Let me know!
Thanks.
The other question that I'll probably get yelled at for is this: is there a huge difference between real monitors and the system I have now? How is it better technically and then audio visually? You hear more sounds in a crisper way?
I went on craigslist yesterday and a guy said he'd sell me a used KRK Rokit RP8 G2 for $400 (a couple months used)... Should I get these?
In terms of an audio interface I heard that audiofire 2 would be a good setup?