I have had the same experience as boombats. I had run the XLR out to my PS-1 XLR in (thinking it would give better clarity for some reason) and all through the first set it sounded like baked ass to quote. As soon as I switched back to the full range out the sweetness was back.
The sound was like a low grade distortion, but not a good musical kind of sound. It was just an experiment, since I'm mis-using the F1-X for the Further I assumed that was the reason, and didn't give it another thought until I read this thread.
To note, if I run the XLR out to my mixing board in the studio (headphones only) this ass sound is not present, but its still not as nice as the 1/4 full range out.