It will *not* do what you want it to do - sorry, it's not really suitable.
It's a transformer box that does MS conversion at line level - the only way you can use it for monitoring from an FR-2 is to connect it to the line-outs and then to a separate headphone amplifier.
You *could* use it with a
Graham Slee Voyager. Use XLR / XLR cables from the FR-2 to the Sonic Orbit - then XLR / inoi-jack lead to the Voyager and monitor there.
Personally, I have an Audio Developments box for this - but it was discontinued a few years ago.