I had 3 different XTCs over several years. I still think it is the best all-around amp I've ever played. It responds to everything - cabs, speakers, tubes, bias-settings, playing styles.
I could never get super-happy with the loop. I got addicted to the sound of the amp with the loop off, and the master around 4, and I was haunted by the clean sound of the 20th Anniversary 6L6 model I sold to fund a Helios.
Make sure to set the GREEN channel master full-up with the mids at around 4, excursion to T and assigned presence OFF. You get the most wonderful Deluxe-on-steroids tone. The secret to the BLUE and RED are not being afraid to run the TREBLE higher than you think since it is an audio taper pot. Love that amp, it is a work of art.