Addition of an unlisted RS-232 device. Custom device addition.

I have a JBL SDP-40 that I would like to control via a GC-100-12 Gateway. Any ideas how to accomplish this? I had been using an iRule system to control but would like to move to Roomie. Thanks in advance for any help.

https://www.roomieremote.com/knowledgebase/is-it-possible-to-add-support-for-a-custom-device/