I tested the oversampled version and compared with the normal version. I'm not able to ear difference with the two version, and i'm still earing the unwanted "bitdowner" effect. The oversampled version consume more cpu, aproximatively two times more.
for the UX2: At this times, my kernel is a generic 4,2 , but i wiped out the line6 module and I installed the line6usb driver from sourceforge. I did that because with the kernel module, if i forget to stop jack before I disconnect the UX2, jack become mad, consume all CPU and my computer become almost frozen.
ps: again, i have an issue to launch guitarix without installing it, but this time, guitarix is unable to find one of its .so