Since I bought this case two months ago, I got the same issue too. The simple answer is: It depends. There are some EATX mainboards, which will fit into the case. They just must not exceed the maximum width of 27.7 cm. I've determined this size yesterday by myself, by measuring the baseplate for the mainboard in the case. I also read a review on a dealers site, where the customer manged to build in an EATX ASUS Rampage VI. I'm thinking about buying a MSI X570 Creation which got the width of 27.2 cm. Hence it should fit into the case without major problems.