I've got a 2003 At 1.8T with the Symphony radio and I'm considering following the DIY to add an amplifier or two to it. What I'm wondering is if the low-level output from the radio to the amp is already crossed-over or if there are low-pass and hi-pass filters in the amp or at the speakers? I want to add an amp to power the sub but don't want to add a crossover if there's already one in place. I also want to amplify the door speakers but only if there are crossovers in place to protect the tweeters.