Suggestions...

Looking for a digi converter to run from my preamp to my comp. Anyone have a suggestion to this. I been looking at a few things and a guy down at the music store showed me a piece that goes from my mixer to the box then plugs via USB. Into my computer. I forget the damn name etc..I been looking at some M-audio fireboxes and what not I just wanted to get a few opinions before I purchase anything on here. Prefer kain or heat or anyone else that has knowledge in the field about it. I'm looking at upwards of 4-5 bills to spend on it but would like to go a bit lower if I can or if somthing a bit cheaper can put out a similar sound. As of now I run RCA to standard quarter inch mic input but it has some feedback. I know the more wires the more feedback will this in anyway be a problem with a converter? Also, If I am running a firebox or somthing of better quality than my current equipment, is this going to restrict the fireboxes potential? Or will the firebox preceed over the equipment, thanks in advance guys.