Updated initial post with 5 GHz additional channel testing.
Below is a list for the RT2600ac US region which ASUS doesn't support all those channels (not even their USB-AC68 adapter I tested). Of course it all depends on your region. Unfortunately it's going to be difficult to find out what client adapters and devices support available channels.
8 Channels (80+80 MHz)
36+155,40+155,44+155,48+155,149+42,153+42,157+42,161+42
16 Channels (20/40/80 MHz)
36,40,44,48,52,56,60,64,100,104,108,112,149,153,157,161
18 Channels (20/40 MHz)
36,40,44,48,52,56,60,64,100,104,108,112,132,136,149,153,157,161
21 Channels (20 MHz)
36,40,44,48,52,56,60,64,100,104,108,112,116,132,136,140,149,153,157,161,165