ISY is not a box, it is a program. 994i is the box. ISY is currently defaulted to install on the Polisy Hardware(which is just a PC from PCengines). Polisy hardware runs FreeBSD as an OS, Polisy the program runs on top of that OS the same as ISY does. At the OS level both programs are unaware of each other. Polisy(the software) is just a connection point for NON-Insteon and NON-Zwave hardware to communicate with ISY. ISY is still the "Brain" that orchestrates the automation. Since the two programs are unaware of each other on the OS they still operate as if separate(different hardware). For Polyisy and ISY to communicate with each other Polisy(program) Needs to find the ISY, if being run on Polisy(hardware) it will just be the IP address and port 8080 with the username and password for the ISY(program)
Now PolyGlots are just small scripts that allow Polyisy to communicate with those other services or hardware(Tesla, Roomba, NOAA, and so on).