I think your phono stage must be a ZP 1 or 1.5 because there is only input option on it.  The ZP 1 was apparently set up for MM cartridges and the ZP 1.5 was set up for MC.  And the ZP 2 has two input options with a switch to select one or the either.  Here is a white paper Steve wrote on the evolution of the ZP 1, ZP 1.5, and ZP 2.  

https://www.decware.com/paper26.htm  

One way you could find out is to remove the plate/s (fastened by screws, not hex bolts) and snoop around for those Sowter step up transformers

By the way, quite a phono stage.  No a fantastic phono stage if I do say so myself.

Good luck with sale

I think you've done the right thing.  Unfortunately, someone else in the community might not get to enjoy the ZP 1.  Unless you would still like to let it go after your assessment.  

Due to the nature of time and mental acuity, I cannot be absolutely, positively certain... but I think that putting one of Steve's phono stages (ZP 2) in my system was the biggest audio improvement I've experienced.  It's really hard to know, but that phono stage re-defined listening for me.

At any rate, glad you are revisiting your ZP 1.  Please let us know your opinions about it.