Hi Steve,
Are you using LabVIEW to grab the images? If so there is an example that will work with the PXI0-1409 that ships with LabVIEW. It is called LL Scan Multiple Channels. This VI acquires images from 4 different camera's. What the example is doing is configuring a buffer for each of the channels.
I hope this helps.

Have a great day.
GG