How to control Outbound isp connections via link controller

In the simplest form it's quite straightforward - create a pool consisting of the routers from each ISP - IP addresses and any port. Then create a Wildcard Virtual Server - 0.0.0.0:0, any protocol unless you want to handle TCP and UDP differently. Disable Address and Port Translation on the Virtual Server (under Advanced Properties) on the VS and asociate the router pool. You probably want to use SNAT Automap on the VS as well.