My config.txt seems ok, dtoverlay=hifiberry_dacplus and dtparam=audio=on removed.
The command amixer returns this (it seems the voulume is set to 0, isn't it?):
/etc$ amixer
Simple mixer control 'DSP Program',0
Capabilities: enum
Items: 'FIR interpolation with de-emphasis' 'Low latency IIR with de-emphasis' 'High attenuation with de-emphasis' 'Fixed process flow' 'Ringing-less low latency FIR'
Item0: 'FIR interpolation with de-emphasis'
Simple mixer control 'Analogue',0
Capabilities: pvolume
Playback channels: Front Left - Front Right
Limits: Playback 0 - 1
Mono:
Front Left: Playback 0 [0%] [-6.00dB]
Front Right: Playback 0 [0%] [-6.00dB]
Simple mixer control 'Analogue Playback Boost',0
Capabilities: volume
Playback channels: Front Left - Front Right
Capture channels: Front Left - Front Right
Limits: 0 - 1
Front Left: 0 [0%] [0.00dB]
Front Right: 0 [0%] [0.00dB]
Simple mixer control 'Auto Mute',0
Capabilities: pswitch
Playback channels: Front Left - Front Right
Mono:
Front Left: Playback [off]
Front Right: Playback [off]
Simple mixer control 'Auto Mute Mono',0
Capabilities: pswitch pswitch-joined
Playback channels: Mono
Mono: Playback [off]
Simple mixer control 'Auto Mute Time Left',0
Capabilities: enum
Items: '21ms' '106ms' '213ms' '533ms' '1.07s' '2.13s' '5.33s' '10.66s'
Item0: '21ms'
Simple mixer control 'Auto Mute Time Right',0
Capabilities: enum
Items: '21ms' '106ms' '213ms' '533ms' '1.07s' '2.13s' '5.33s' '10.66s'
Item0: '21ms'
Simple mixer control 'Clock Missing Period',0
Capabilities: enum
Items: '1s' '2s' '3s' '4s' '5s' '6s' '7s' '8s'
Item0: '1s'
Simple mixer control 'Deemphasis',0
Capabilities: pswitch pswitch-joined
Playback channels: Mono
Mono: Playback [off]
Simple mixer control 'Digital',0
Capabilities: pvolume pswitch
Playback channels: Front Left - Front Right
Limits: Playback 0 - 207
Mono:
Front Left: Playback 0 [0%] [-99999.99dB] [off]
Front Right: Playback 0 [0%] [-99999.99dB] [off]
Simple mixer control 'Max Overclock DAC',0
Capabilities: volume volume-joined
Playback channels: Mono
Capture channels: Mono
Limits: 0 - 40
Mono: 0 [0%]
Simple mixer control 'Max Overclock DSP',0
Capabilities: volume volume-joined
Playback channels: Mono
Capture channels: Mono
Limits: 0 - 40
Mono: 0 [0%]
Simple mixer control 'Max Overclock PLL',0
Capabilities: volume volume-joined
Playback channels: Mono
Capture channels: Mono
Limits: 0 - 20
Mono: 0 [0%]
Simple mixer control 'Volume Ramp Down Emergency Rate',0
Capabilities: enum
Items: '1 sample/update' '2 samples/update' '4 samples/update' 'Immediate'
Item0: '1 sample/update'
Simple mixer control 'Volume Ramp Down Emergency Step',0
Capabilities: enum
Items: '4dB/step' '2dB/step' '1dB/step' '0.5dB/step'
Item0: '4dB/step'
Simple mixer control 'Volume Ramp Down Rate',0
Capabilities: enum
Items: '1 sample/update' '2 samples/update' '4 samples/update' 'Immediate'
Item0: '1 sample/update'
Simple mixer control 'Volume Ramp Down Step',0
Capabilities: enum
Items: '4dB/step' '2dB/step' '1dB/step' '0.5dB/step'
Item0: '4dB/step'
Simple mixer control 'Volume Ramp Up Rate',0
Capabilities: enum
Items: '1 sample/update' '2 samples/update' '4 samples/update' 'Immediate'
Item0: '1 sample/update'
Simple mixer control 'Volume Ramp Up Step',0
Capabilities: enum
Items: '4dB/step' '2dB/step' '1dB/step' '0.5dB/step'
Item0: '4dB/step'
Thanks for your help