I used another grommet (not shown in your picture) about 16" to the left of the grommet you circled, at the same height.
CAREFULLY cut a couple of crossed slits with an Xacto, above the existing wires in this grommet. If you don't make the cuts too big, the grommet will seal around the wire pretty nicely. I was able to simply push the wire through, and it ended up on the passenger side floor. I then was able to route it up into the center console, and from there to the sub and amp under the driver's side and passenger side seats. I really wanted to completely stay away from the brake pedal, accelerator, etc.
There is no insulation inside the passenger compartment behind this grommet.