The second half of this video by 'rail engineer' magazine shows the BAM equipment being used and it suggests to me that all the larger green machine is doing is pulling the track off the train behind it, and aligning it with the first few rollers so that the smaller machine can guide the rail as it moves forward. The clipping is done by blokes walking along with powered clipping machines.
http://www.youtube.com/watch?v=VHWuTvpcco4
As far as I can work out, this means the sleepers must be accurately aligned across the gauge width, and the ballast depth very accurately set, as they don't seem to be lifting the sleepers at all.