...... (a) with the same amount of force (F) -- which, by Newton's second law, means reducing its inertial mass (m).
There is no way that impulse engines can reduce mass for the Saucer section, or indeed, reduce mass for anything other than the exhaust gases produced by the impulse engines. I have the same manual, and I still don't see how you can get to your conclusion.
The driver coils are localised and specific to the fusion reactors that they are connected to. No connection to warp anything. You seem to be confusing the ability to drive gas jets to near warp velocities with driving a ship to warp. Impulse cant do that, no matter if you strung all the driver-coils together.