Hey Bob,
The input impedance is 10k ohms so unless you have an unusually high output impedance on your preamp, that should be fine.
If you're having a pair of custom cables made and you don't expect to be using them for anything else, you might as well have them made with the correct XLR connections for the Otari.
The conventional is;
Pin 1>ground
Pin 2> hot
Pin 3> cold
The Otari is;
Pin 1 >ground
Pin 2>cold
Pin 3>hot
There's a diagram of how to connect to RCA cables in the manual.
I doubt if having those switched will make an audible difference since it's an absolute phase issue but like I said, if these cables are dedicated for your Otari, why not?