S50 pro + audible low level hiss only through optical input

I have an audible hiss when when no content is playing but only when I am using the Toslink input through my S50 pro+. Content plays normally but when it stops then my speakers have a low level noise that is pretty annoying.

The sound is present even when i lower the volume of the S50 pro+ to 0

The hiss is not present when I am streaming through the S50 pro+ directly.

I use the S50 pro+ as a preamplifier for two channel audio when I am using my LG projector.

Please suggest possible solutions and reasons for the issue.

Setup details:

Nvidia shield connected to projector through HDMI

LG HF85LA projector connected to S50 pro+ through optical

S50 pro+ connected to emotiva Basx A2 power amplifier

Everything powered by the same powerstrip

No antennas in close proximity

I think this is a phenomenon of the cheap dsp solution of arylic products, this noise also exists with the A50, unfortunately it can do so much for so much money…

Can arylic confirm this low level noise on the s50 pro+ many of us are experiencing using it as a pre-amp, does not meet it’s claimed S/N of 110dB at low volume levels?

@Marcel unfortunately I don’t know, I have just an old s50 pro and I mostly listen to radio streams on it as well (my home theater amplifier has a network player and I use it as the main player). I think that these cheap devices are compromise solutions, They do not replace technically well-built, but therefore more expensive systems. If sound quality is important, it is definitely worth getting a dedicated external DAC. There are some interesting measuring datas about Arylic S50 pro here: Arylic S50 pro measurements and comparisons | Audio Science Review (ASR) Forum