Mike when I connect the panel directly to the radio I seldom need to put the audio gain knob about 50%. With it operating remote, and the knob turned all the way up, I can barely hear the audio. I realize this is a very subjective measurement but I would say that the audio volume when turned all the way up is less than 1/2 what I experience when the panel is connected directly to the radio.
What ground wires are you referring to?