Not sure about the exhaust being piped in from speakers. Haven't heard that one. Just the engine noise but that uses the sound tube on the intake.
You had the wire running from the remote out on the lc2 to the remote on the sub amp? Not 100% sure it will send a signal if you dont have a remote wire running to the lc2 so what you are doing might be the only way if you dont use a remote wire to the lc2. I would just be afraid of coming back to my car with a dead battery.
As for the front speakers. I definitely would not recommend cutting them as the bass up front is really nice feature and it really adds to the sound. I would just splice into the line to get the signal.
https://www.amazon.com/Morris-Produc...s=quick+splice Those should do.
Once you do this your subs will wake up and sound 10x better. I was about to return my JLW6 until I moved it from the rear deck to the front speakers. I just unplugged the deck speakers at this point. They weren't really adding anything.