I've not yet found a way to configure exactly what I want, but by now I do have a workaround:
I installed the alsa-tools
package: "A collection of console-based utilities for specific sound hardware". When I open it thorough terminal and press F3 I can control the volume gain with the vertical cursor keys and with each strike I change 1% of the gain! :)
So, my hot-key-combination is Alt+Tab (to the terminal window with AlsaMixer) + Up (or Down) for a 1% volume change.