The same problem. I don´t have sound in the computer with El Capitan. In addition when I instal the drivers in El Capitan, my computer restarts all the time. Only stop when I disconnect the UX1.
It is a problem because I like a lot the new OS X but I just stay in Yosemite only for the Line 6 drivers...
I will wait one week more to the new drivers but I am already thinking change/sell my UX1.