Try something like this. Initialize and setup both instruments and then issue a single GET. The way you're doing it, you are sequentially triggering one instrument and then the other. I've never done a GET with VISA only the function from the GPIB palette. Instead of the GPIB Trigger function, you could try the VISA Assert Trigger with the resource name of the GPIB board or the VISA Send GPIB Command function with GET as the command. Sorry, but I don't have any instruments available right now to try it with.