I think they did get the through MU working. It would have been a very heavy load for 2 Set motors if they hadn't. I was referring to the 4 S motor set returning home when they coupled the two motor pairs back to back for the trip back to Flemington. With out some sort of adaptor magic, back to back power cars can't MU to one another.
Yes, when coupled up as S/S/AK/AK/AK/S/S, the MU wiring is connected through the entire consist. However, the electrics have 44 wires, the AKs have 27 loco wiring. By chance, there are 27 critical circuits, so they are all connected. Things like doors are not connected.
This took some trialling to prove that it would work. The first trial was 4 car S/AK/AK/4 car S set. Then we had 3 car S/AK/AK/ 3 car S set. The final version is 2/3/2.
The above and special S set motor consist runs under a TOC waiver. Only the 2 leading motor cars power during the transfer to/from the AK cars, the rear 2 just act like trailer cars. When coupled up to the AK cars, all 4 motor cars provide motive power.
The next running of S/AK cars will be March/April 2014. It is anticipated that there will also be a mid-year and end of year run (as per the 4-monthly cycle to record the network).