2015 Prius 4 with the factory JBL Greenedge system. I've seen the notes from people who have attempted to make changes to the factory speakers in the JBL system. Since the extra Greenedge amp not only amplifies and crosses over the signals between the speakers, changing out the individual drivers doesn't work out. I like the idea of adding one or two of the small enclosure subs that can be mounted under the front seats. My only question to anyone that has done this is other than adding a larger speaker(s) for the lower frequencies, how does it help the other drivers in the car. As I see the setup, I would be tapping into the + and - speakers for the front bass drivers to send to an amp for the sub. All of these systems offer a crossover to only allow the frequencies below a certain point to the sub but aren't you still sending that full range to the front drivers? Part of the beauty of subs in a system is it takes the work of those low frequencies away from the smaller bass drivers and allows them to only work on the "mid-bass". Unless there was a powered sub that offered a passthrough of the high level output and would cross over that amplified signal back to the in door drivers, I don't see a way around that. I'd thought about bass blockers for the remaining speakers but the lowest frequency model I've seen (150Hz) would actually work at about 300Hz at the ~2 ohm load the speakers are running at. I think that's a little high for a sub to pick up the difference. I know some have done this already and the reports I see here are it's worth it. Maybe I'm overthinking this and should just hook it up and let my ears decide?