Although express talk supports multiple lines, I have never tested trying to make concurrent calls through the command line interface (unfortunately I am not at home right now so I cannot test what happens). I don't think it would permit more than one call, but as I said I will have to test this later.
However, for what you are trying to accomplish, may I suggest using NCH's IVM software instead? It is better suited as an auto-dialer and has many built-in features to make the process easier and more integrated.
Also, if you want to use different SIP lines like you are suggesting... your best bet is to use NCH's Axon software (it is free of charge). This is essentially a VoIP PBX call management system that supports features such as dialing plans.