When using ADAT sync with a FireWire 1814, ProjectMix I/O, or ProFire Lightbridge, follow these steps to set the sample rate prior to launching your recording application:
 

1. On the Hardware tab of the FireWire control panel select “internal – digital inputs muted” with the FireWire 184 and ProjectMix I/O; and select "internal" with the ProFire Lightbridge.
    
2. Make sure the desired sample rate is set and locked (in the Control Panel); when recording at sample rates 88.2kHz or 96kHz, enable S/MUX after setting the desired sample rate
3. Set the desired sample rate on the external ADAT clock source device
4. Select ADAT sync in the FireWire control panel
5. After the sample rate is locked, launch your recording application

 
It is recommended that you turn down the volume on your speakers and/or headphones to avoid potentially loud digital distortion associated with the momentary sample rate mismatch.  If you need to change sample rates, close your recording application and repeat these steps.