Apologies for the delay in reaching out to you!
Angelle is right in that a image of your Focusrite Control settings would be ideal so that we can see the routing you have selected. Also are you what are you choosing for the Driver type in Sonar?
Just to confirm you are monitoring playback from your computer speakers and not speaker monitors connected directly to your Scarlett 6i6
Ideally you should be using the Scarlett 6i6
as your Input and Output device since it is the way that you are able to get high quality audio to and from your computer.
If you are still having issues with audio playback, I think that it may be best to open a ticket with us here : https://support.focusrite.com/hc/en-gb/requests/new
This will allow us to do some more in depth troubleshooting!
David // Focusrite Technical Support