i think you know better how to handle this...

i added those lines as child of 'dynamic' field of 'symfony_cmf_routing' (or 'cmf_..') into app/config/config.yml

        instances:
            - symfony_cmf_routing.orm.dynamic_router
            - symfony_cmf_routing.dynamic_router

the chain -> routers_by_id tells which router and priority, they are not all dynamic one but the dynamic should be setup by the extension if i understood correct.
should another field (say 'dynamic') be added to mark a router as dynamic? the provider info are into xml services config and this tells which repository should the router fetch from.