I have a JVC KD-Dv500 head unit. It plays everything, including dvd's. It is dolby 5.1 ready, w/ the digital toslink output. I am looking at a PhoenixGold 5.1 amp for everything except my sub, that has the toslink input. SO, my question is, it I hook up the head unit to the amp with the digital cable, would I still need to use RCA's, or does the digital cable take the place of them? MattB