My primary use of iFly on my Surface is for on-the-ground planning so I haven't hooked up an external GPS. I assume iFly will use the GPS of an external system, like Stratux or Skyguard. If so, you might want to focus on the network issue. The first ADS-B systems used port 43211 and I would guess Srratux uses it as well. 4000 may also be in play. AP could confirm the ports used by their supported systems. In the meantime, follow these instructions: http://amiduos.com/support/knowledge-base/article/network-ports-forwarding-in-amiduos.
After loading try:
Duosportforward add ifly1 UDP 43211 43211
duosportforward add ifly2 UDP 4000 4000