I've got an XL-ATX motherboard (TRX40 GIGABYTE AORUS EXTREME) in a Tower 900. The board overlaps the cable hole rubber grommets by a few mm (like in the level 20 xt), so I took them out. It's possible that some nylon spacer washers to raise the motherboard slightly would enable the grommets to stay, but I wasn't bothered about them.