I can not choose the Roon DSP mode

Support
5

Here is the guide:

Digital volume control always requires some use of DSP power. The question is where that does happen.

  • Fixed volume: Volume controls within Roon are disabled.
    • Use your (pre-)amp/speakers buttons, wheel or RC to control the playback volume of your system.
  • Device volume: Roon sends volume control commands to your audio device. It’s up to the audio device to respond to the commands and use its DSP to perform the requested volume changes (or in rare cases probably use an exposed analog volume control).
    • A mode that could work with the OP’s audio device but “In the Rose RS250 in the software setting the volume switch is set to ‘off’.” – needs to be on for that.
  • DSP volume: Roon does all the volume processing.
    • Not available for the OP (I assume the RS250 is used as a networked [Roon Ready] audio device by the OP).
      Note: Because of potential issues with buffering and latency, this option is usually not available for networked audio devices (by design), but can be used with built-in (soundcard) or locally connected (USB) audio devices on endpoints running Roon, Roon Bridge or Roon Server.

Regardless of the audio device setting above, Roon may always perform “static” (for the song/track) volume leveling and/or headroom adjustments if configured.