You can’t forward packets from Dashbox to HA at this time. I chatted with Ben @ Brultech about this and did some troubleshooting on my own and hit a wall with some errors in siobrultech-protocols (https://github.com/sdwilsh/siobrultech-protocols). You should be able to get the GEM talking to directly to HA. You can then try to forward the packets from HA to Dashbox. Ben put together some sample (untested) code: https://github.com/BenK22/homeassistant_dashbox_forwarding/.
I have not tried it yet.