How to remap mouse button in debian?

Question

Debian

Hello! Tell me how to reassign or duplicate the multimedia buttons of the asus n53sv laptop to additional. mouse buttons.
Specifically, the combinations Fn + Left, Fn + Right (player control) are of
interest. I thought through xbindkeys, but the Fn button itself does not give an output when checking the button code through xev.
When you press the same combination,
I get

KeyRelease event, serial 41, synthetic NO, window 0x4c00001,
root 0x94, subw 0x0, time 19005853, (168,-5), root:(1074,37),
state 0x2010, keycode 171 (keysym 0x1008ff17, XF86AudioNext), same_screen YES ,
XLookupString gives 0 bytes:
XFilterEvent returns: False

Those. the combination is interpreted, the songs are switched.
Add. mouse buttons give their codes, 8 and 9 respectively.
The question is how to make it all work?