I reached out to their support last time and the following was their answer.
Hope this helps:
If you want to keep the old board you could use an Interface kit. However, it will be only able to read one the zones on a doubling senario. And I’m not sure that board could be setup for a programmable zone to monitor the status of the alarm or a keyswitch for remote arm/disarm.
In that case, I’d recommend a Conversion kit. It would be simplier and allow you to use all the zones as well as full control. However, you will lose the old keypad.