How to set VolumeUp, VolumeDown and mute shortcuts on Lubuntu?

In my config (~/.config/openbox/lubuntu-rc.xml) are my multimedia keys set like:

<!-- Keybinding for Volume management -->
<keybind key="XF86AudioRaiseVolume">
  <action name="Execute">
    <command>amixer -q sset Master 3%+ unmute</command>
  </action>
</keybind>

With xev I checked, those are right keys.

But it does not work. AFAIU, problem is that my soundcard setup has no Master device.

Output of amixer scontrols:

Simple mixer control 'IEC958',0
Simple mixer control 'IEC958',1
Simple mixer control 'IEC958',2
Simple mixer control 'IEC958',3
Simple mixer control 'IEC958',4

I tried like:

amixer -q sset IEC958 3%+ unmute

but it does not affect volume level.

If I run alsamixer, it does not seem look good:

┌────────────────────── AlsaMixer v1.1.3 ──────────────────────┐
│ Card: HDA Intel HDMI                 F1:  Help               │
│ Chip: Intel Haswell HDMI             F2:  System information │
│ View: Playback                       F6:  Select sound card  │
│ Item: S/PDIF                         Esc: Exit               │
│                                                              │
│                                                              │
│                                                              │
│                                                              │
│                                                              │
│           ┌──┐     ┌──┐     ┌──┐     ┌──┐     ┌──┐           │
│           │OO│     │OO│     │OO│     │OO│     │OO│           │
│           └──┘     └──┘     └──┘     └──┘     └──┘           │
│        < S/PDIF >S/PDIF 1 S/PDIF 2 S/PDIF 3 S/PDIF 4         │
│                                                              │
│                                                              │
│                                                              │
│                                                              │
│                                                              │
└──────────────────────────────────────────────────────────────┘ 

As you may see, there is also no way no trim volume.

Volume app on start bar works fine, also pavucontrol.

But how to set keyboard shortcuts to work with my setup?

Lubuntu 18.04, Lenovo Thinkpad X240, lspci:

00:00.0 Host bridge: Intel Corporation Haswell-ULT DRAM Controller (rev 0b)
00:02.0 VGA compatible controller: Intel Corporation Haswell-ULT Integrated Graphics Controller (rev 0b)
00:03.0 Audio device: Intel Corporation Haswell-ULT HD Audio Controller (rev 0b)
00:14.0 USB controller: Intel Corporation 8 Series USB xHCI HC (rev 04)
00:16.0 Communication controller: Intel Corporation 8 Series HECI #0 (rev 04)
00:16.3 Serial controller: Intel Corporation 8 Series HECI KT (rev 04)
00:19.0 Ethernet controller: Intel Corporation Ethernet Connection I218-LM (rev 04)
00:1b.0 Audio device: Intel Corporation 8 Series HD Audio Controller (rev 04)
00:1c.0 PCI bridge: Intel Corporation 8 Series PCI Express Root Port 6 (rev e4)
00:1c.1 PCI bridge: Intel Corporation 8 Series PCI Express Root Port 3 (rev e4)
00:1d.0 USB controller: Intel Corporation 8 Series USB EHCI #1 (rev 04)
00:1f.0 ISA bridge: Intel Corporation 8 Series LPC Controller (rev 04)
00:1f.2 SATA controller: Intel Corporation 8 Series SATA Controller 1 [AHCI mode] (rev 04)
00:1f.3 SMBus: Intel Corporation 8 Series SMBus Controller (rev 04)
02:00.0 Unassigned class [ff00]: Realtek Semiconductor Co., Ltd. RTS5227 PCI Express Card Reader (rev 01)
03:00.0 Network controller: Intel Corporation Wireless 7260 (rev 83)