Audio problems with Asterisk, XLite, and Polycom 501

I have a Linux box with Asterisk, behind a router. I’ve configured an X-Lite softphone and a Polycom 501, but can’t seem to work past one-way audio problems.

When I call the VoIP line in *, I have full duplex audio between telephones. That’s great.

But placing calls from either the softphone or Polycom result in the called party not receiving audio.

I’ve opened up the requisite ports within the router, but the problem persists. I’m pretty green to all of this…help?