I also have a 9260-8i and noticed this behavoir on both an Asus Z68 and MSI X299 board. Luckily somebody on the net found the solution, so i just registered here to spread the news:
Press Ctrl+H at the RAID card's boot messages, then press the key for bringing up the bios boot menu (usually F8 or F11), then select your RAID-controller as a boot device -> LSI WebBIOS will show up instantly.