Dear Goal-tech,
Thank you for contacting National Instruments.
To address your question, multiple device synchronization has the same theory as single device synchronization. The trigger signal can be routed via the RTSI bus, and remember to connect the devices with a RTSI cable.
Configure both Digital Input and Digital Output for start trigger and connect the same start trigger to both trigger pins (ACK1/STARTTRIG1 and ACK2/STARTTRIG2).
Then use Trigger Config VI within the output task, and configure the output so that it controls the digital input. The output task will be the master and the input task will be the slave, and they will be synchronized through the REQ lines of the RTSI bus.
I included an example because this can be confusing.
I'm assuming you're using Traditional DAQ as DAQmx isn't supported with the 6533.
Let me know if you have any further questions or if this does not resolve your issue.
Thanks again and have a great day!
Chad AE
Applications Engineer - National Instruments