I just installed this DIY software, and it looks damn impressive. Perhaps it has a steep learning curve though. Also, I can't confirm its accuracy yet without testing. All that said, it looks stunning from the webpage. I discovered it by pure chance when doing a google search recently. Here is the link:
http://kimmosaunisto.net/Software/Software.html 
WARNING: This is not my software, so usage is at your own risk!
I'm looking forward to messing with it though.
Comments
I am using the raw OmniMic phase data (not minimum phase data). My modelled Z offset in XSim is 1.33 inches (33.782mm), so I entered this as the woofer Z offset and left the X and Y values at zero. I get a very good match to my XSim on-axis model. I noticed that you can enter a large number of off-axis curves and offsets and then click back & forth as needed. So I plan to load my XSim off-axis data and test this next.