I'm glad I've found this post BEFORE purchasing the router. Thank you, Tech9.
My netwerk is based on a RT-AX88U main router, 1 RT-AX88U on the second floor (aiMesh), and 1 RT-AC88U (aiMesh). (please don't ask why there are 2 good equiped routers placed in an aiMesh setup ;-) ).
I just need one...