> Maybe you sould try "xev" (that's what I use, anyway).
Xev doesn't detect if there's no scancode.

Problem fixed by using setkeycodes instead of udev hwdb rules. I used
setkeycodes method from the wiki:
https://wiki.archlinux.org/index.php/Map_scancodes_to_keycodes
mapping scancodes 0xA5 and 0xA6 to free keycodes, and it returns me a
keycode, so I can use any configuration tool, TDE panel works well
now.
The strange thing is that mapping the same scancodes to keycodes by
udev hwdb rules maps the keycodes... but not to the keys pressed, yet
to my "Previous song" and "Stop" multimedia keys!
No idea what's going on, sticking with setkeycodes.
MCbx