There are two different ways that you can get a signal into the R1004: high and low level input. Low level input is measured in voltages and comes in the form of RCA outputs from the back of your receiver, going to the RCA inputs on your amplifier. High level input is measure in wattages, and comes in the form of one positive and one negative wire from the back of your receiver, going to the input terminal of your amplifier in the same wire form. Low-level (RCA) input wiring is preferred for best audio performance. Always use a high-quality RCA cable for the best audio performance. NOTE: Do not connect both the high and low level inputs from your receiver to your amplifier at the same time.
Properly setting the gain on your amplifier is key to getting great sound in your car. The gain control is not for adjusting volume - it simply adjusts the amount of signal that is coming from your receiver and going to your amplifier. If you set it too high, you are introducing distortion into the sound, but if you set it too low, you are choking back on what the amplifier is there to do in the first place. A technique that works on most amplifiers involves first turning the amplifier’s gain all the way down. Turn on some music and turn up the stereo's volume until you hear distortion. Then turn it down until the distortion goes away. Go to your amplifier and turn the gain up until the distortion comes back, and once more back off until the distortion goes away.