Hi lcc0610,
Can you give a try by setting below commands before starting the playback.
#For speaker playback
amixer -c 1 cset name="x Stereo DAC MIXL DAC L1 Switch" "1"
amixer -c 1 cset name="x Stereo DAC MIXR DAC R1 Switch" "1"
amixer -c 1 cset name="x Speaker L Playback Switch" "1"
amixer -c 1 cset name="x Speaker R Playback Switch" "1"
amixer -c 1 cset name="x SPOL MIX SPKVOL L Switch" "1"
amixer -c 1 cset name="x SPOR MIX SPKVOL R Switch" "1"
amixer -c 1 cset name="x SPOL MIX DAC L1 Switch" "1"
amixer -c 1 cset name="x SPOR MIX DAC R1 Switch" "1"
amixer -c 1 cset name="x Speaker Playback Volume" "0x20"
#For headphone playback
amixer -c 1 cset name="x Stereo DAC MIXL DAC L1 Switch" "1"
amixer -c 1 cset name="x Stereo DAC MIXR DAC R1 Switch" "1"
amixer -c 1 cset name="x HPO MIX HPVOL Switch" "1"
amixer -c 1 cset name="x HP L Playback Switch" "1"
amixer -c 1 cset name="x HP R Playback Switch" "1"
amixer -c 1 cset name="x HPO MIX DAC1 Switch" "1"
amixer -c 1 cset name="x HP Playback Volume" "0x20"