Sort of …
I’ve done it with two separate ADI-2 DACs, one via RCA and one via XLR - something I chose to do because some sources (and/or amps) don’t always behave well when you make multiple connections between them. Additionally some sources don’t behave well if you connect more than one output at a time*.
While it is more work to compare, you should try listening to the single-ended output from your DAC feeding the single-ended input on the Phonitor X without the XLRs connected, and then swap the connections and try the balanced side (without the RCAs connected). This will ensure you’re not running into funky issues with the source and/or interactions with multiple connections to the same amp from the same source.
What DAC are you using, by the way?
With the Phonitor X, while the balanced and single-ended paths measure differently, I can’t reliably tell the difference in listening and generally use the balanced input and output on it as my primary connections.
(In case you’re wondering why I don’t use the balanced output from my DAVE into the Phonitor, it’s because I have that feeding my big tube amp).
*For example, my original Yggdrasil would not emit any sound if I had the single-ended output connected to my old WA5-LE and the balanced to an iFi Pro iCAN unless the Pro iCAN was switched on.