If you are talking about simultaneous measurements, dual mics wouldn't help there. You can do separate measurements and average them. You have to be careful how you do that though. I have done that before, and I might have even done that with the Klipsch sub, but I did that measurement a while ago and forgot how I did it exactly. The problem is that lower frequencies are less affected by the direction than higher frequencies. So, for example, if I placed the mic facing the driver at 2 meters, I would still get a good amount of port output. However, if I reversed the sub for the mic to be facing the port side, I would not get nearly as much driver output as I did port output for the opposite orientation, and that I because the driver produces higher, more directional frequencies than the port. This is easy to overcome in CEA-2010 testing, by just using the highest numbers for any measures orientation at measurements taken from the same distance, but it's a bit more challenging when trying to get a frequency response that fairly reflects the performance of the sub. It can still be done, although it might introduce a slight bit of inexactitude in the measured response. One way to overcome it would be to measure the sub at a very far distance, like 10 meters, but this sub doesn't have the output to overcome the environmental noise of an outdoor measurement at that distance.
