Scott

The best way to implement your requirements to make routing decisions based on source address is to configure Policy Based Routing. With PBR you can look at traffic to be forwarded and make forwarding decisions on factors other than just destination address - especially based on source address.

I would suggest that the way to implement this would be to set up a default route pointing at one of the outbound links (if one link will carry more traffic than the other it may be best to have this be the active default route). I would then configure a floating static default route so that if the primary default route fails then traffic will fail over to the other link. Then I would configure PBR. To do this you would configure an access list which will identify the traffic for different routing. Then configure a route map which will use the access list to identify traffic and will then set ip next hop to send the traffic out the alternate link. And then you configure ip policy on the interface on which the traffic arrives at the router.

HTH

Rick