Others on this forum have been setting these up, and 3CX used to have a manual setup guide dedicated to this device range however it has been removed - as you are probably aware these devices are un-supported.
Either way you will need to set the device up in 3CX as a "Generic" Gateway, select the amount of lines you wish to use and main trunk number and setup the Cisco manually to register to 3CX.
A little more work than a fully supported gateway like a Patton or beroNet but you should be able to achieve it.