Gonna go with Nomad, as well. Nomad is faster, smarter, and pound-for-pound more powerful than the DM. With its greater speed and maneuverability it wouldn't be too hard for Nomad to avoid the DM's anti-proton beam (which can only fire forward after all). I suspect that Nomad's weaponry, which was far in advance of a starship's, could eventually batter its way through the DM's hull. Failing that, Nomad could probably vaporize planetary chunks before the DM could eat them, thus "starving" the DM to the point of impotence.