Volume keys on Asus T100 with Spiral XFCE ubuntu

I've just recycled and old Asus T100 transformer by installing a Spiral XFCE linux distro. The goal is to use it for videos. It works mostly fine, but I still have trouble for volume setting : The volume keys on the tablet do not work at all (even though it seems to have been working out of the box for some people cf http://www.jfwhome.com/2016/01/04/latest-steps-to-install-ubuntu-on-the-asus-t100ta/ ) If anybody has any idea how to fix this, it would be great ! If there is no solution to that, a way to have the keyboard volume keys work without having to press the "fn" key would be great too. I found a few ways to tweak the setting, mostly related to fnlock_default in /sys/module/asus_wmi/parameters (cf https://forums.linuxmint.com/viewtopic.php?p=2247849#p2247849 ) but none of them seems to be working. Any idea ?