amp gain w/different box, grounding kits?

Ok. Yea all of my grounding points are very close to each other. Out of those 3 amps, only 1 amp has a ground loop problem but its only the 3rd and 4th channel. It cant be a grounding problem then. All of the amps grounding wires are the same gauge as their power wires. I just thought that just maybe by having more than 1 grounding point would help the amps alittle more. But if my amps already have good grounds along with the correct ground wire gauge, then there is no point. But I will still get a grounding kit to mount under the hood. Just 1 more question. How can I check to see what voltage is coming out of the sub output on the headunit? Do I simply use a DMM to those RCA cables or what? And if you use a DMM, can you please explane what setting to have it on and so on, because I have no clue how to use them. Very sorry. But thank you.

How good are those voltage stabilizers that I see on ebay?

Does anyone know anything about the voltage stabilizers?

audioboy2007 asked the same question "voltage stabilizer" in which 'ground kit' was answered.

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