Quote Originally Posted by KeithGTP03 View Post
Tag the lines on the input of the factory amp....it is full range going into the amp and it is filtered and amped coming out of it. You'll get a cleaner signal tagging those lines.
This is what i was thinking too. If it was an aftermarket deck, the amp preoup would be the pure signal with no changes at all. The amped signal would actually be fine to work with but not filtered. But I've not found any information anywhere to tell me for sure or not if the signal is filtered.