jezus its like children fighting in the sand pit in this thread!
Never knows best. your username is rather accurate. you are trying to tell someone that they are doing something wrong (which they are not doing wrong), just because its not how you would do it.
8 speakers on a 4 channel is not out of the blue by ANY means! there is nothing fucking wrong with using his head unit, it maybe 10 watts but maybe thats also enough power for the speakers that its powering. they could be 1inch away from his ears for all you know... AND IT IS NOT WHAT THIS THREAD IS RELATED TO AT ALL
stop being a smart ass. It has been proven by many people that it gets you nowhere
now that my post 18hour shift rant is finished... try dd1ing with out the line driver, sounds like you were using that as your meter before the dd1 so try it with out. if your getting really shitty voltage and you do need it, then by all means put it back in, the reason why we are suggesting to try it without is that it is just another device that has the possibilty to make the signal dirty which is what you don't want
turn the knob all the way up and then test again, you could test with out the knob then plug in. but I dont suggest it at all because then you are tuning the dd1 against what your actually going to be using which is the point, the knob might also make the signal dirty for some unknown reason so best to test it with it. now, if you are still having the same trouble. try it with out the knob. if it then works like I said earlier go get yourself a lc1 they are cheap as heck and will do excatly what you want it to do!