I have an XP-27. I use both outputs simultaneously when I am recording a record. RCA to my A to D converter and XLR to my preamp. I'm sure you can use both outputs in an XP-25.
I tried out a SUT (!:15 Bobs Devices) to see if my Lyra Etna SL would sound better that way versus the MC settings. I much preferred the MC settings without the SUT in the middle. YMMV.