I think you call it a potato and I call it a spud haha.
My advice comes from hooking an analizer up to the amp and adjusting both inputs and outputs to achieve optimal signal quality.
I have no idea what type of system he is working with or how many amps in cascade he has. But from my experience the levels I suggested is what I have found to be best, not just what Blonder Tongue suggests.
Here is a link(not discussing these particular amps but a rough idea on how to calculate) that will give a rough idea of what your looking at so that you can determine yourself what your levels should be. The best way to determine this is to hook an analizer up to it and determine what you need for your specification. But in my world what I suggested is what has worked best for me. In my opinion input level does matter.

http://www.sencore.com/uploads/files/SignalLevels2.pdf
If you need more information to support my suggestions please feel free to shout.