dallcock I apologize for the extreme delay, for some reason I didn't see your reply at the time and have only now logged in to check on the responses. In our case, we are trying to control an external arbitrary waveform generator via PCI-e. We are planning to do this as @sb10q suggested. In our case, semi-unpredictable latency will be difficult, but not impossible, to get around. We will use PCI-e to program the AWG on the fly, but we can probably trigger it separately with a TTL pulse, hopefully getting the best of both worlds (programmability and timing precision).