Do you happen to know how I can route the wav-audio to the DAC (pin 25) on the core2?

I tried with the wav player template by @lukasmaximus or @lukasmaximus89 ... but the result is that the firmware of core2 doesn't seem to know the I2S modes...

any suggestions what to do?

If your trying from the SD card the documents say the path is sd/somefile.wav not /sd/somefile.wav (no preceding forward slash)
however this assumes that somefile.wav is stored in the root of the SD card. also the wav file has to match certain file requirements that are a restriction of MicroPython.

I get errors when trying to initialize i2s device:

"type object 'I2S' has no attribute MODE:MASTER....

from machine import I2S
import os, uos
from wav import wave

#initialize the I2S device
i2s = I2S(  mode = I2S.MODE_MASTER | I2S.MODE_TX | I2S.MODE_DAC_BUILT_IN,
            rate = 16000,
            bits = 16,
            channel_format = I2S.CHANNEL_ONLY_RIGHT,
            data_format = I2S.FORMAT_I2S_MSB)

#uncomment the following line if you have issues mounting the sd
#uos.sdconfig(uos.SDMODE_SPI,clk=18,mosi=23,miso=19,cs=4)

#create a function to play the wav
def wav_player(fname):
    wav = wave.open(fname)
    i2s.set_dac_mode(I2S.DAC_RIGHT_EN)
    i2s.sample_rate(wav.getframerate())
    i2s.bits(wav.getsampwidth() * 8)
    i2s.nchannels(wav.getnchannels())
    i2s.volume(20)

    while True:
        data = wav.readframes(1024)
        if len(data) > 0:
            i2s.write(data)
        else:
            wav.close()
            break

# Playing WAV audio file
lcd.clear()
lcd.print('working',0,0,0xffffff)

try:
    uos.mountsd()
except:
    os.mountsd()
    lcd.print('sd card not mounted',0,50,0xffffff)
    pass

while True:
        wav_player('/sd/test.wav')
        i2s.stop()
        wait(5)

I have another error on line 39:

module object has no attribute 'mountSD'