Best answer by AjTrek1
Your connections should be Turntable > to Pre-Amp input > Pre-amp output > Connect input.
Setting line-out to pass through on the Connect is only to allow level control (volume) of a device it's connected to using the Sonos app. However, the target device has to be pass-through capable.
Try setting Connect to variable then set the level on the pre-amp to slightly above comfortable listening level and use the Sonos app w/Connect to adjust level up or down. Setting sound to uncompressed may help :?