Also I am setting my amps and have been told to use a DMM to set the gain, I got this email from JL support telling me what to do.
the first and most important thing to check is that the input sensitivities of the amplifiers were set up correctly .. Use this guide to be sure along with a target voltage of 17.4 for each pair of channels for the XD400/4 and 34.6 volts for the XD600/1 .. http://www.jlaudio.com/header/Suppo...rial:+Input+Sensitivity+(Gain)+Setting/287546 .. Now for the dials , try setting the HIGH PASS filter frequency dials on the 400/4 to 80 hz and set the SLOPE to 12 db for each pair of channels . Now for the 600/1 set the LOW PASS filter frequency dial at 80 hz as well and set the SLOPE to 12 db .. This should improve the sound and transition between the main speakers and subwoofers ..
As long as I disconnect the speakers and have the appropriate tone playing through the cd player (1 khz for speakers, 50 hz for subwoofers) nothing can go wrong, can a Digital Multimeter damage the amp at all? I only ask because if there is risk I would get someone with more experience to do it (I don't want to ruin my equipment from making a ignorant mistake!)
P.S I am a complete newb trying to learn more about car audio