Ok, this is not a thread for liking or hating the new engine room, let keep the discussion to figuring out it all works. WE can do it.
Based on what we saw, it appears they ejected either multiple cores or multiple reaction assemblies or chambers or something. I didn't see exactly where they ejected from nor did I get a good look at what was in motion when Scotty flipped his switch. (cannot wait for screen-grabs!)
Then we had a line about diverting power from the nacelles to the shields.
Plus the nacelle roots themselves attach directly to the shuttle-bay.
My preliminary theories: Multiple redundant small reactors in the secondary hull provide power to the ship. Part of that power is diverted either as electrical current or plasma to the nacelles where the further power generation/amplification takes place.
Prehaps that's why that the nacelles are so large. Not only are you housing the warp coils themselves but additional power generation hardware.
Lastly, the "surge" of power when the ship jumps to warp... prehaps this generation of warp drive was open-loop... the plasma was discharged into space after reacting with the coils. Makes sense based on what we saw yes? Later designs collect and recirculate/recycle the plasma, a closed loop design. That design could come a few years down the road, maybe a decade or two later.
As for the differences between the engines of the NX-01 and the NCC-1701... NX was very early technology... it was advanced in some regards but it just couldn't scale up to Big Ship designs so they went for a more brute force method.
Thoughts? Comments? Please remember this is a technobabble thread not an OMG I HATE THE NEW DESIGN DEATH TO JJ thread.