Don't quote me on this, but I believe the Axe TX is CCPM mixing only. It will send signals to aileron, elevator, and pitch with each stick movement. I've seen someplace on the internet where somebody has a USB connector cable and a box with a chip that removes all the mixing signals so it will work with Flight simulators. That could be your problem.

Here's a link

http://www.milehighwings.com/usb_cables.htm