Just got my 420 installed and I am happy to be able to say I have ZERO engine noise - at any volume. It works great and I am completely happy with this purchase. However, I have a few questions on the operation of unit.
1) When I turn down the boat speakers, I seem to loose the sub. Is that normal? I would think not since there are 3 separate RCA inputs (high, low and sub) on the back of the 420.
2) Do most people crank the volume to max on both the tower and boat speakers and then vary the master volume on the head unit, then use the 420 to reduce either the boat and/or tower speakers?