Helm Bolt USB DAC low volume

Hi,
I have an issue with my new setup using RPi 4 with a Helm Bolt USB DAC.
The Bolt is connected to my NAD amplifier with a 3.5mm to RCA cable.
On Volume playback (Internet Radio and Airplay), the output Volume is very low.
When I connect the Bolt directly to my phone, I have very good signal level.
Is there a setting to increase the output volume?

Version 2.882
Mixer set to Hardware (Software or nothing makes no difference)
Volume set to 100%

What am I missing?

I want to sort out my basic set-up before activating paid subscription to get Tidal Connect MQA…

Thanks

Klaus