They are driven as uni-polars but are really just normal, push-pull drivers with two stators on either side of the pentagonal electret film. The schematic for the adapter shows just a simple input to the transformer and output again. I just noticed that Sony had included the impedance specs for the transformers 3?:4100? which works out to a step up ratio of 1:36.97
The other uni-polars I've owned had a single stator and a metal backing plate connected to ground. That's what Phillips uses at least.