low volume of the sources compared to the players

I write from  regarding a problem we have with a B400S player installed at one of our customers.
Basically it is a restaurant divided into three areas (rooms) in which there are video monitors which tune into the various TV channels via a satellite TV decoder (and another digital terrestrial TV decoder). The optical output of the satellite decoder is connected to our B400S bluesound player for audio reproduction which then passes through the audio system with the various amplifiers.
The problem is with the audio playback volume.
When I play audio through the B400S from a radio channel or through a music service eg deezer or spotify the audio is quite good and loud and loud and still allows me to turn it up more if I want the volume. That's all fine, then the problem begins when the source becomes the optical output of the satellite TV decoder which would then be the optical input of the B400S player. In this case, even at maximum volume on the various player channels, the volume remains very low and does not there is also a way to raise it by raising the volume of the satellite decoder. Same thing with the digital terrestrial TV decoder (RCA audio output digital terrestrial TV decoder B400S analog audio input) the volume remains too low in the output of the B400S players and the amplifier is not able to work at a satisfactory volume. The drop in volume is very high almost more than half almost 2/3.
By setting the switch to microphone input mode of the B400S instead of line as it should be done, the system goes into saturation and does not work, a strong hiss is heard.
What can we do to increase the input volume of the B400S player?! Is there a solution to that?!
Thanks