I looked at a Thelios, they have great info on GitHub including top-down images of the system internals, https://media.githubusercontent.com/media/system76/tech

I looked at a Thelios, they have great info on GitHub including top-down images of the system internals, https://media.githubusercontent.com/media/system76/tech-docs/master/src/pictures/thelio-major/thelio-major-b1/thelio-major-b1_internal-diagram_config.png https://media.githubusercontent.com/media/system76/tech-docs... On this one you can see they use a Gigabyte X299 Aorus Ultra Gaming Pro. However, it's common to do replacements, so am exact model is only going to be possible with bespoke systems IME. Did you try asking, most people only want a specific bundle of features and don't care about the model numbers per se.