There is an existing grommet with factory wiring passing through it just below and to the RIGHT of the battery (see the white and yellow wires). Just poke a dull round tool (a phillips screwdriver will work) next to the factory wires to open up the grommet a little, and pass your new wire through it....
It will exit behind the glove box, high in the passenger side foot area...
Now you can continue them over to the dash or stuff them under the carpet going back to your amp via the transmission tunnel or door sill areas.