I had the same issue with asus recovery utilities. But I managed to use tftp come with windows 8 to downgrade tm-ac1900 to older firmware and able to follow Engineer instruction to install merlin. I used Asus CFE and mtd-write v2 to update CFE.
My router is running with merlin version 3.0.0.4.376.47_0 and the initial page shows RT-AC68U instead of TM-AC1900.
Thanks
My router is running with merlin version 3.0.0.4.376.47_0 and the initial page shows RT-AC68U instead of TM-AC1900.
Thanks