Now you're seeing my point.
If you are hearing (while recording) the dry guitar through the mixer, AND the processed sound at the same time (with the track monitor switch ON), then there should be a way, using the mixer controls, to mute the DRY guitar and hear ONLY the processed signal from the DAW. Every dedicated Audio Interface provides this function. It could be that your MIXER is designed to output both at the same time, but not either/or.
What model Soundcraft mixer do you have? I'll check the manual and see if I can figure out what's up.