Hi Alex,
did the last test. i been downgraded the kernel to 4.0.0 rc3  it was working
kernel on g5 quad . i been used it to made this guide in past you can see it
here:https://ubuntuforums.org/showthread.php?t=2274612&p=13269146#post13269146 

i have the same issue reported as before nothing change with swapping the
kernel

Ciao
Luigi