I have a line out converter and thats the way I did it. There is a little trick with mine though that made the subs "work" i guess would be the best word. I can only have one rca cable plugged into the amp or else the bass is extremely distorted and they sound blown. When just one is in bass hits clean and sounds great, not sure why because I hooked up a converter for my buddy and his works fine with both attached.
Mods: 5% tint rear 35% front, debadged, black tails, black headlights with halos and HID, Pioneer touchscreen dvd, all speakers replaced with JL, JL 12" sub, black wheels, blue calipers, CAI, exhaust