Alright, so I went out and bought analog jacks to plug into the XT Pro, thinking it may have been the stereo connectors, and still, under settings, series, and parallel, I get sound output, with no change in audio loudness when I adjust the tube amp gain. (The tube amp is working, using the FX loop on my guitar amp, I am able to get a very warm, clean tone from it, the volume knob is fully functional, so it is processing the audio signal)
Well, I thought, maybe the FX loop is only for digital output. Maybe it has no effect on the analog output.
So I interfaced it into my computer, using Cubase LE, changed the audio so it was recognizing a stereo signal, strummed the guitar, and saw the levels rise on the mixer, in cubase, meaning, it was seeing output from the XT Pro.
I then hooked in the tube amp to the XT pro FX loop, and tried adjusting it's output and watching the signal graph, and it had zero effect on audio output, with either series, or parallel selected int he XT Pro.
Do I have a broken FX loop or something? What's the deal? I could understand of maybe the connecters were damaged on the inside, but according to the manual, I should have *no* sound output when "Series" is selected in the FX loop setup menu, and I have not only analog audio output, I also have digital!
What's the deal? Is there some special setting somewhere to enable the FX loop?