I tend to agree that MJ designed the action to be going on the nacelles. However, certain episodes (such as That Which Survives
) clearly point to a single area of reaction between matter and antimatter.
In a MJ-nacelle style setup though, I believe that the ship could
enter Warp even with the lithium crystal circuits all blown. However, since things like inertial dampeners and deflectors would be unpowered at this point, you really wouldn't want to!