OUT-1 1/4" DIRECT feed from the X-Amp's Class-A circuit. This output should always be used to ensure proper grounding.
(Taken from http://www.radialeng.com/di-xamp-features.htm)
I posted the same thing in the paragraph above yours.
Im surely going to have to play around with Output 1 when troubleshooting since it seems to say that RF issues are more likely to come into play if nothing is grounded on Output 1.
But I would sware that the only reason I went to Output 2 was because I had less of a problem with the RF noise.
Only one way to find out.