I'll backup the chip tomorrow and save the configuration to my desktop PC.

Thanks for the help.

sory here is the full link to the setup intructions for the amp: https://learn.adafruit.com/adafruit-max98357-i2s-class-d-mono-amp/raspberry-pi-usage

I'm going to post here the result of a few lines of commands, hoping that it will help to understand...

lsmod command return me this:
Module Size Used by
bnep 12051 2
hci_uart 20020 1
btbcm 7916 1 hci_uart
bluetooth 365780 22 hci_uart,bnep,btbcm
evdev 12423 2
joydev 9988 0
brcmfmac 292632 0
brcmutil 9863 1 brcmfmac
cfg80211 544609 1 brcmfmac
rfkill 20851 4 bluetooth,cfg80211
xpad 16908 0
ff_memless 5315 1 xpad
snd_soc_hifiberry_dac 3230 2
snd_soc_bcm2835_i2s 7480 2
bcm2835_gpiomem 3940 0
snd_soc_pcm5102a 2310 1
snd_soc_core 180471 3 snd_soc_bcm2835_i2s,snd_soc_hifiberry_dac,snd_soc_pcm5102a
snd_compress 10384 1 snd_soc_core
snd_pcm_dmaengine 5894 1 snd_soc_core
snd_pcm 98501 5 snd_pcm_dmaengine,snd_soc_bcm2835_i2s,snd_soc_core,snd_soc_hifib erry_dac
snd_timer 23968 2 snd_pcm
snd 70032 6 snd_compress,snd_timer,snd_soc_core,snd_pcm
uio_pdrv_genirq 3923 0
fixed 3285 0
uio 10204 1 uio_pdrv_genirq
uinput 9125 0
fuse 99603 1
ipv6 408900 34

amixer cset numid=3 0 return me amixer: Cannot find the given element from control default

cat /proc/asound/cards return me :
0 [sndrpihifiberry]: HifiberryDac - snd_rpi_hifiberry_dac
snd_rpi_hifiberry_dac

Wow, It's been a while... So thanks for your answers: I will park my 'dedicated DAC' idea and simply pull the audio from the HDMI!