Running wires through firewall

[deboxster]

I am upgrading my Bose stereo with Kenwoord Excelon X393 head and Alpine PDX 5 amp, replacing the MOST based Bose and CDR23. I figured out most of the electrical wiring, but need to thread a six wire (Monster) RCA cable from the HU to the amp through the firewall. I found some info, but no clear picture of the best place (grommet) to pull the wire through. Any suggestions are very welcome. I will post my experiences once I have completed the job.

Thanks for any hints!