Could you please give me an advice

You can go headphone out to aux in. Seriously crappy. Or USB out to a DAC to aux in. Garden variety crappy. But I believe that you will be impressed.

Cannot advise on sub without info.

On many receivers, if you use a left/right analog source, it will NOT process the sound and send the bass to the subwoofer.  It will just pass-through the left/right signal to only the main left/right speakers. You may want to start reading the documentation for your Onkyo receiver.  You might be able to switch to a different decoding mode (such as Dolby Music or DTS:Neural:X).

Thank you very much for the help and reply above, I will study the manual again. thanks