Live as ReWire master
If you want to use Live as ReWire master, start Live first.
Once the program has finished loading, you can launch the second application, which will automatically run as ReWire slave.
By pressing the play button in either the master or the slave application, both DAWs will playback in sync.
To hear the audio generated from the DAW running as the slave, create an audio track in Live and select the ReWire slave in the track's Input Type chooser ("Audio From" drop down menu). Additionally, enable Input Monitoring for this track.