ENDIAN Firewall - Multi-WAN pre-install question

Ok... I have a multi-wan router and 3 isps connected.

ISP1 is a single static ip cablemodem
ISP2 is a 5-static ip cablemodem
ISP3 is a single static ip T1 line used for failover outgoing internet in case isp1 and 2 are down.

So... I can set my router to dmz all the ips to any lan ip such as endian or whatever...

One of the statics on ISP2 goes to our mailserver, 1 to our webserver and 2 tp our dns servers where the 5th is used for outboung web browsing.

How would be the best way to set all of that up in endian so that incoming mail makes it to our mail server and outgoing goes back out over the correct wan ip ?