Hi, yes you are correct. The VM167 has 5 analog inputs.
For 8 thermocouple I recommend the CANTool. You can connect an ECUMasters 8 channel thermocouple amplifier, https://www.ecumaster.com/products/egt-to-can/.
Thats very disappointing, The code and screen is setup is for 8 extra channels and the plugin page says "This plugin provides support for the inexpensive VM167 board. With this plugin and the board, 8 more analog channels are added, as well as support for 4 outputs.". This was one of the reasons I purchased Yourdyno. Please amend the plugin pages description of this for others.