Volume control in xfce.

When I touch the sound volume keys of my keyboard, I see a slider
popping up, moving in response to the key presses. However, the sound
volume does not change at all, because they move the headphone volume (I
can see that in alsa mixer).

Where can I control to which channel is those keys attached to?

This is XFCE in 12.1, using pulse.

partial output from hwinfo:

Hardware Class: sound
Model: "Creative SB1040"
Vendor: pci 0x1102 "Creative Labs"
Device: pci 0x0009 "[SB X-Fi Xtreme Audio] CA0110-IBG"
SubVendor: pci 0x1102 "Creative Labs"
SubDevice: pci 0x0018 "SB1040"
Driver: "snd_hda_intel"

Cheers / Saludos,

Carlos E. R.
(from 12.1 x86_64 “Asparagus” at Telcontar)