98 GMC Suburban, power through firewall

Hello everyone. I just bought a new 98 GMC Suburban.  I am going to put im my 15'' JBL and Power Aqustic amp.  There is one problem.  I am not sure where to run the power cable through the fire wall?  There is obviously not any open holes to run it through :(  I have done some looking and I might be able to drill a hole about 3'' below the where the steering linkage goes through.  The only thing is that I am not sure if I should be drilling a hole in my fire wall or not?  Or if I could some how run it under the car and up into the back that would work to.  I was just wonder what you guys think would be the best way to do this?

I have done some looking and I might be able to drill a hole about 3'' below the where the steering linkage goes through.  The only thing is that I am not sure if I should be drilling a hole in my fire wall or not?

Yes, this will get you through the firewall, just be sure you drill to the side of the brake booster and not into it. And also use a grommet to ensure your power cable doesn't rub against the metal and wear the shielding off.