Ah, then what are preamps used for then??

So, lemme get this straight - I connect soundcard into the amp, something like this http://rotel.com/products/specs/rb1070.htm and then to the speakers? No preamp needed, just RCA cables from soundcard to speaker? And I could adjust volume and all from the soundcard's mixer? Sorry for bein' dense, but I wanna make sure I get this right and don't have to ship stuff back after I find out it doesn't work.