@TIN_MAN - LOL
@Mytran - my questions exactly
I figured Spock's "death room" was part of the "mains", perhaps the "main energizer" where it has been bypassed due to radiation. It could be the equivalent of the energizer that houses the dilithium crystal in the S2 engine room. I mocked one up just for kicks
Of course, the reason we've never seen it blast radiation out in TOS is because the Enterprise had never been so critically hit like that in TWOK.
In TMP, it could be the energizer was on a different deck (like in TOS S1) and moved to where we see in TWOK and like you guess that there is alot of unseen machinery below decks, IMHO.
I wonder about that big isolation door as well as it was down when Scotty took the mains off-line but we didn't see whether it was back up when Spock got the mains back on again. Could it be just a pressure door for people? and it is transparent to the energy conduit? Hmmm