A gas turbine engine assembly includes a turbine section having first and second turbines mounted for rotation about a common rotational axis within an engine static structure, first and second turbine shafts coaxial with one another and to which the first and second turbines are respectively operatively mounted, first and second towershafts respectively coupled to the first and second turbine shafts, an accessory drive gearbox mounted to the engine static structure, and a transmission transitionable between a first mode where an electric machine is driven at a first speed relative to the first towershaft, and a second mode where the electric machine is driven at a different, second speed relative to the first towershaft.