Mykol,
Pwaring is right, For what you are doing it is better to get a good hardware firewall. ZA works fine for me, but then I'm not doing all the Heavyduty things that some are doing here on AO. It sounds like it's time for you to un-grade to hardware.
This subject has come up many times before. Do a search here on AO or take a look at the bottom of the page and is if the ghost of AO came up with anything. Then do a search on google for more insight. But, Pwaring is probably right, get a hardware firewall.

Freddy