Reply to Traktor S4 with Rokit 8's?

I got a question i know it might be a little stupid to you guys but is it ok for me to hook up my KRK Rokit 8's directly to my Traktor S4 using 1/4 " chords... i have done it and it works and all but even if i crank my Traktor all the way up it isn't very loud... if I get an audio interface would it make my sound louder? if so... what interface do you suggest for an Ableton, Traktor, MacBook user with a medium sized room for under $200? I really don't know too much about speakers and it seems as if everything is a little complicated, sorry for wasting your time and space on this community but just need this quick question answered so i can replace my shitty speakers with these KRKristmas presents...