I thought it just controlled the rca level, has no effect on the gain? Thats why with it all the way down theres no sub sound at all and with a bass knob there will still be output
they do this from heat...yes the d series can be used under the hood, but a little batt like that needs some protection. The heat wrap made for batteries works good. My d975 did the same thing (not as bad)
see if you can talk him down a little...I bought one set brand new in box like 1.5 years ago for less then that, and another slightly used set for less then that recently