Is it my cables...i really need to know?

ok im using reg. rca cables and i can hear the music comein out of my speaker but its very soft...and all i can really hear is static...i just want to know if i really need to get the digital cable...cause on the back of my tv it says coax(digital audio out) so do i need to get a digital cable...and on the back of my system it just aux in...if u can any help will be helpful...thanks in advance