Master/Slave Link Summary

[Axel]

I have just posted this over on the 1000 Pro launch thread, but to keep it in context, it is worth repeating here:

I did ask about the master companion link. Apparently the SPDIF to AES can be utilised with either a 75 or 110 ohm cable, or something in between. At first, I was told 'it makes no difference', apparently because the AES/EBU has an input transformer that makes the input effectively blind to cable impedance, however, apparently a cable with a transformer is theoretically the ideal. (such as the Audioprana?)

Any idea as to why it would be ideal to have two transformers in the signal chain? What does the transformer on the cable do? Convert 110 ohm to 75, or vice versa?