I have tried to control the volume via TV but have not been successful. The current setting is as follows:
The optical cable (SPDIF) of the TV (LG C2 OLED) outputs TV sounds to Raspberry Pi 3B+ and HifiBerry DAC + DSP (HifiBerry OS; DSP version 14). Then DAC + DSP sends analog signals to the speakers via RCA cables.
The current issues:
1. I could not control the volume from the TV. Without change the CURRENT_MIXER_CONTROL setting, I only managed to get a constant volume. I cannot control the volume from the TV nor HifiBerry OS.
2. I tried to change CURRENT_MIXER_CONTROL="DSPVolume" and this resulted no sound coming out from the speakers.
I wondered if you could help me here? Please let me know if any further information is required.