"Add to that that we only see the front two pads, and I'd suggest that what we are seeing is a smaller, auxiliary room instead of the usual one(s).
Perhaps this is the Transporter Room that is used when saucer separation occurs? Those impulse engines are not in the same league as M/AM reactors, a small T-Room is probably all they can handle!"
Unorthodox but wonderful idea, I love it!
(but that's probably not the only transporter room in the saucer?)
In "Mudd's Women" they used the transporter while without M/AM power. So maybe Spock's "How many coming?" doesn't refer to the amount of dilithium crystals, but shows a concern if they still have enough power to beam that many people from Rigel's surface.
Same goes for space station K-7. I believe this one to be powered only by nuclear fusion and the two transport pads in Mr. Lurry's office could suggest that fusion power will only allow beaming of two people at a time.
As for the transporter room studio set I'm not exactly sure what we are talking about. The Season Three set in general had this odd "kiosk" corner protruding into the room of whatever you'd call it, like in "The Way to Eden": http://tos.trekcore.com/hd/albums/3x...edenhd0104.jpg
(hmm...shouldn't the console be visible in this shot: http://tos.trekcore.com/hd/albums/3x...edenhd0166.jpg
The scene in front of sickbay, however, doesn't look like the transporter room set extended into
the corridor: http://tos.trekcore.com/hd/albums/3x...edenhd0474.jpg
(I don't think they would have moved the wall back just for this scene, but I could be wrong, of course).
I can't shake the feeling that during Season Two they had this turbo lift access in the corridor at the expense of the back part of the transporter room set.
By Season Three the turbo lift got back to the end of the circular corridor and rather than re-assembling the transporter rom set as seen in Season One they came up with these design changes for Season Three. Measure?