Hi Javi, I bought the cable for my Onkyo TX-RZ830. Unfortunately it didn't say anything about the size of the plug? So I would have to buy a jack adapter 3.5 to 2.5. Whether it works afterwards, I would have to test first. The specifications for the IR receiver jack plug 2.5 are missing. Without this information, I don't know if the plug will fit. You must check whether the Swisscom box has an IR input 2.5 or 3.5. TechniSat only lists their own compatible devices.
Sorry that I can't give you any better information.
The product description says that it is made for external IR receiver. Unfortunately, I can't tell you if your specific Onkyo receiver has one, since there are several different models. It's best to check the user manual of your device to see if it has one. If not, then this will not fit.
To be on the safe side, I would always use the IR receiver of the corresponding manufacturer. The technology is usually the same but the pin assignment, the IR frequency and the plug size may differ.