In terms of the correct ports to forward, I believe it is:
5060 UDP (or whatever Axon is set to as the SIP port, may be best to forward 5060-5070 to be sure)
8000-16000 UDP (by default this is what Axon uses to communicate, the fact you don't have 8000-8010 forwarded could be the source of the problem since I believe these would be the vital ports necessary.
Also if you are still having trouble, Axon has a couple of advanced options that usually fix problems with 1 way audio. E.g. the "Always relay audio feature" and one of the other features (can't remember name) that says beside it that it corrects 1-way/no-way audio issues.