Going to mention this again as there are alot of posts in here. I dont recommend taking line level from anything but the front ch feeds. I am almost certain the rears (and 3rd row) have a highpass filter. this will kill your low end response. sub frequencies run from 20hz-100Ish, If the rear speakers are in fact filtered, they will be filtered around 80 or possibly higher. If the feed is filtered at 80 hz (depending on rolloff) you will be missing the main portion on the sub band. Again I have to assume as the fronts in my xlt do the majority of the low end and the 3rd row (if parallel are so tiny they would really need to be controlled) As for the sony system I would be getting the high pass feed on the sub ch before the factory amp.