Hello @Morten_Valbjorn,
Unfortunately, I do not believe you will be able to play DSD files to the Onkyo NR656 from a PC or Linux computer. Since there are no HDMI drivers on Windows or Linux that support native DSD, you have to use the DoP format for DSD on HDMI. As far as I can tell, the Onkyo will not decode a DoP formatted DSD stream via it’s HDMI inputs.
When you play a DSD file to the Onkyo via HDMI connection, Roon will automatically convert the stream to a high resolution multi-channel PCM stream. This should still provide excellent sound quality.
-John