I listen to music primarily from my PC via Toslink optical out to a powered speaker set which has optical inputs (toslink and co-ax digital) as well as analog inputs. The optical output has been free from PC Mobo noises, it's nice.

I am upgarding to Trend TA10.1 and passive speakers. Therefore, I thought it is a good idea to continue using Toslink with a DAC to isolate mobo noises. Hence I ordered the Super DAC pro with a Trends 10.1.

I tested Super DAC pro by connecting a Toslink optical cable from PC Toslink out to the optical input of the DAC. I then use RCA plugs to connect the audio outputs of the DAC. The other end is a stereo TRS 3.5mm plug which is plugged into my power speaker analog input. I use the front speaker input of the set of 5.1 inputs.

When I plug in DAC power, the red LED lights up indicating power OK. When I plug in optical cable into the DAC, the green LED lights up indicating audio normal. Everything seems to be good so far. However, the speakers don't output music but some kind of "square wave" sounds. They sound like cricket calls. I used to produce time codes in audio streams. Time codes are square waves. These codes play back as audio like cricket calls.

I suppose that the Super DAC pro expects Toslink signals and would convert digital audio signals into analog form which can be amplified to drive speakers. My setup follows the idea but it does not produce the expected results. What have I missed?

Any inputs will be appreciated. ( I don't know anything about the Ethernet like jack marked as "balanced in" "Ctl", is there anything essential here ?)