I also did this for years on my XTL, X3L, and now my HD500. Regular guitar in the the guitar in, variax in the VDI. Turn down the volume on the guitar not in use. Set the input parameter to variax + guitar. I used the same main patches for both. I also for a few years used a 3rd guitar -- an Ovation acoustic/electric on the Aux In, but I only set the Aux In (think I used Variax + Guitar + Aux) active for the acoustic patches I had set up for that guitar, so I had 3 guitars plugged in at once with the X3L and HD500. It was good that I just pulled the guitar off the stand and rolled up the volume and was good to go. You do have to remember to roll off the volume in the guitar you're not using, as often you will get sympathetic sounds from the guitar on the stands -- kind of embarrasing and annoying...

Dave