Hi mdillon,
If you go to ni.com and enter '6733' in the Search field then you will be linked to the product page for the PXI-6733.
Once there you can look at the link for the User Manuals for this device.
You will want to take a look in https://www.ni.com/docs/en-US/bundle/ni-6711-6713-6722-6723-6731-6733-features/resource/370735f.pdf . Once you open this file simply search for '6733 impedance' and you will see that the Input Impedance for a powered-on PXI-6733 is 0.1 Ohms.
You can also find the specs by using the Contents Tree of the Help file and navigate to
Analog Output Series Help > Device-Specific Information > NI 6731/6733 > Specifications
I hope this helps you,
