Wrong. You will be sending a high level signal to a low level input. You need a step down converter (line out converter) to do that. It will step down the high level to low level. But you might as well leave it be if you're going to do that. You wont notice any difference. To get sub control from your HU, you need to connect rca's from the sub preouts on the back of the HU to the rca input on the amp.