Most HUs that have a dedicated set of preamp outputs meant for subwoofer use will also feature an independent level control that only affects the sub outputs (like your 7875....wanna sell me the faceplate off of that, by the way?)
Most of your higher end HU out there have that feature. All of the Kenwood Excelons's do. It is nice to have. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif