thanks for clearing that up.... instal guy said i might need to buy one if my amp didnt have one... luckily it does... yes, im a nooballows you to get signal to your amps through your HU's speaker leads instead of using RCA cables. It's generally considered a secondary option to standard rca's, but if you want to keep your stock HU high level inputs can be a good way to avoid incorporating an external Line output converter (LOC).