The Xert Player for Garmin ConnectIQ requires that you configure the trainer as part of the app.  You need to select it in the app in order to get Trainer Control.  Unfortunately, due to the restrictions within the Garmin ConnectIQ environment, the power and speed data collected from the trainer cannot be stored as regular data in the activity generated.  Instead it is stored in developer fields which is a feature available to ConnectIQ apps.  The field is tagged as a power/speed data field and so Strava and other apps are able to see it as power data but it is up to them to interpret and parse out this information.  All data coming from the trainer is treated this way.  Power data coming from a power meter is not affected.
We are looking to address this issue in upcoming releases of the Xert Player.