Question about setting gain with a DMM

JAYNO20

I have an older Rockford Fosgate 500.2 unit (2002 model) and I had some questions about setting the gain. Everything I have read shows to take the RMS wattage X the ohm then get the square root of that. My only problem is since my amp is technically a 2 channel I am wondering how I do this with it in bridged mode.

That wouldn't normally be an issue aside from the fact that this amp also has a left and a right gain control. Now the amp is 500 RMS x 1 at 4 ohm bridged OR 125 x 2 @4ohm stereo. How would I go about using a DMM to set these gains as close to perfect as possible?

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