1. A method for controlling a powertrain system comprising a multi-mode transmission configured to transfer torque among an engine, torque machines, and a driveline, the method comprising: in response to an output torque request: executing a dual closed-loop control scheme including determining an engine-based output torque range employed in a first feedback loop and simultaneously determining a control acceleration-based output torque range employed in a second feedback loop; controlling engine commands responsive to the engine-based output torque range and simultaneously controlling a control acceleration responsive to the control acceleration-based output torque range to achieve an output torque of the powertrain system responsive to the output torque request.