ENDIAN Firewall - Asterisk >> Endian >> SIP Trunks not working

I have a switchvox PBX behind an endian firewall that isn't working quite how I need it to. I need to NAT 173...148 to 192.168.10.10, but whenever I configure SNAT, the pbx hangs trying to figure out it's IP (unlike asterisk, this does not allow you to edit configuration files, so no, I can't get any of them for you). If I remove SNAT, it takes the address of the endian machine (173...145).

I need to be able to register with a SIP trunk, and allow remote phones to register to the PBX. Is this even possible? Hope so, because aside from SIP not working (and whats new...), its a wonderful piece of software.