No sound when TV is off

I’m quiet new to OSMC. I just switched over from pi musicbox for video output. But I’d like to listen to music without turning the TV on, which doesn’t work. I have the hifiberry dacplus installed.
thankful for any help

cheers

config.txt file is:

gpu_mem_1024=256
hdmi_ignore_cec_init=1
disable_overscan=1
start_x=1
disable_splash=1
gpu_mem_256=112
dtoverlay=hifiberry-dacplus-overlay
sdtv_aspect=1
gpu_mem_512=144
dtparam=audio=on