[SR-Users] two way routing

Hello I am looking at the following configuration: 1/ voip providers, with different external sip servers, will send calls to kamailio, that will dispatch them to asterisk servers, with load balancing & failover. The IP of the asterisk servers are known and fixed. 2/ the asterisk servers will also place calls, going through kamailio, that will dispatch them to the voip provider sip servers, based on R-URI / Prefix. I've achieved #1 with dispatcher module, I've seen carrierroute module that can achieve #2, but I dont really grasp how to put the two together. I have the feeling that #1 can also be done with carrierroute, and that I only need to check if the 'from' domain is one my asterisk, and chose a different routing table, but I dont see how to do that is that a valid approch ? where should I look to do that ? thanks J.