If you don't have a DTS CD to test with, the simplest thing on the Sonos to do which *should* ensure bit-perfect between what goes into the Sonos and what comes out of it is to go into the settings for that zone and ensure the digital output volume is set to Fixed. I've previously confirmed bit-perfect in my system with the volume set to Fixed. The only issue now is you have to use two remotes to control the system.

Living room: DSP5000.3
WFH Office: M33
Bedroom: P200ZQ