Hi Peter, with the healthy 0.56mV output of the Benz I would set the SUT for 1:10, that will load it well and should provide the best sound.

Use for a good while to get the sound quality imprinted on your mind before you think of any changes.
If you use the 1:20 ratio you will be putting a big signal into the phono stage and losing some of the headroom.

Cheers,
Alan