Every sink in a session is designed to playback in sync regardless of the output type.
That being said there currently are some scenarios where playback can be perceptibility out of sync.
- The output device is connected by something that has a high latency and that latency is not negotiated (ie HDMI, Bluetooth, etc).
- The network paths to each output device have high differences in round trip time.
We currently have the ability to manually adjust the sync between output devices but is only used for internal testing and the setting is not saved. Eventually we plan on making this feature a public part of the configuration client. Feel free to add it to the feature request list to increase its priority.
If you do not fall into one of those categories then submit a bug report.