Hey @harry_masoni,
Would you mind to give us more info about your setup - use this FAQ as a guide ?
Based on the manufacturer’s website CAT is a streamer/ripper/nas and it requires a DAC to be connected to it. What device is connected to your music server?
Also, If you want to playback music with a Sound card/DAC connected to your iMac - you need to enable zone which are under ‘Connected to this Mac’ section.
Thanks