I moved your post off the FAQ. The FAQ Emporium is for answers only.
Ask questions in other forums.
I mounted my DSATX uby drilling holes in my case where the moutning holes for the DSATX are and secured it using some nylon 1/4" nylon spacers between the DSATX and the case, capped with acron nuts
Check the link in my sig to my worklog to see some pictures (albeit not very good pictures!)
The best way to get your cables through the firewall is to pull.
Seriuously, it all depends on how many wires and the thickness. You may be able to run them through an existing hole int he firewall that's grommeted. If you have a lot of cables or ones that are too thick to go through an existing hole, then you may need to drill your own. Don't forget to put a grommet in there to protect the wires and keep out dirt, water, etc.