I've just loaded up my version of the Zavoli software, and by default it will show only 3/4 cylinder options, with no ECU connected.
I can go back in to the main menu and load a previous configuration which is 5-6-8 cylinder, and then go back into the vehicle options and it then shows 8 cylinders.
If you haven't already saved a 5-6-8 cylinder file (which you probably won't have if you've never had it connected) then it won't let you (that I can see) make a 5-6-8 cylinder config.
However if you were to be able to connect to the ECU, then it would download the current settings from the ECU and it would show up in the vehicle settings as being an 8 cylinder install.
Have you ever had it connected to the ECU? Silly question, but the USB-serial cable that's used to connect to the ECU... have the correct drivers been installed for it? Windows sometimes installs generic USB-serial drivers, but they need to be the actual ones that come with the software.
'06 4.2 Supercharged Black/Cream "Jess" -- Bought April 2021 (NZ)
'01 4.6 Vogue Black/Lightstone "Snog" -- Bought Jan 2012
'99 4.6 HSE Cobar Blue/Lightstone -- Sold March 2009
'95 4.6 HSE Epsom Green/Tan -- Traded June 2008