Adding a sub an its amp
I am not that great when it comes to stuff like this, but I think I can hold it down. I have an 07 G6 GT coupe with a monsoon system. What I want to do is to leave the existing monsoon amp and speakers for now and just install a sub and a new amp to power that sub. I have a few questions about it.
First, is there any accessible hole in the firewall that I can run my power cable through without drilling a new one?
Second, is there a way to make sure that the new amp doesn't drain the battery when the car is not on? Can I make it so that the new amp and sub only turn on when the car engine is on?
And last, is there a way to add on this amp by splicing or rerouting existing wires that go from the head unit to the monsoon amp? In other words, can i splice the remote turn on lead wires, sending it to both the monsoon amp and the new amp, and are there patch cables that run from my head unit to my monsoon amp already that carry specifically low-pass signals for bass that i can simply reroute to the new amp, leaving the mid-range and tweeter signals alone and plugged into the monsoon amp? How would I go about doing this?