Headphone output too low

Hello, I set all registers of the ES8388 to output max volume but the playback through the headphones is not loud enough. I got the ESP32 Audio Kit V2.2 2957 with ES8388 Codec and the old variation where I2C is on IO 23 and IO18 instead of IO33/IO32.

Reading the ES8388 User manual https://dl.radxa.com/rock2/docs/hw/ds/ES8388%20user%20Guide.pdf starting from page 22 I've set the Registers like this:

ES8388_WriteReg(ES8388_DACCONTROL3, 0b00110010);
ES8388_WriteReg(ES8388_DACCONTROL7, 0b00000110);
ES8388_WriteReg(ES8388_DACCONTROL4, 0b00000000);
ES8388_WriteReg(ES8388_DACCONTROL5, 0b00000000);
ES8388_WriteReg(ES8388_DACCONTROL24, 0b00100001);
ES8388_WriteReg(ES8388_DACCONTROL25, 0b00100001);
ES8388_WriteReg(ES8388_DACCONTROL26, 0b00100001);
ES8388_WriteReg(ES8388_DACCONTROL27, 0b00100001);
ES8388_WriteReg(ES8388_DACCONTROL20, 0xB8);
ES8388_WriteReg(ES8388_DACCONTROL17, 0xB8);

I think the ES8388 Headphone Amplifier works for testing, but not for listening to music through headphones or there is a change in hardware which is not reflected in the software which controls it.

Is there any resistor which can be changed to fix it or might it be possible to just wire the output of the NS4150 http://inder.cn/WJXZ/nsiway/InderNS4150EN.PDF amp used for each speaker to the headphone jack to get a decent volume. Do you think thats possible? I dont want to damage anything, and my knowledge about the electronics is not good enough to say it will work. Couldn't it just be done by attenuating the amplifiers output via two resistors per channel? or with little trimpots?

Ths is the schematic of the speaker amplifier: esp32-audio-kit_v2.2_sch.pdf

Here is a schematic which shows a connection of headphones in parallel to speaker output: https://www.ti.com/lit/ds/symlink/tpa6030a4.pdf?ts=1661932852771&ref_url=https%253A%252F%252Fwww.google.com%252F

-paul

Ai-Thinker-Open / ESP32-A1S-AudioKit

Headphone output too low #36