@LWM MLO is the only way to have them use more than one channel at a time.  I have two computers on MLO one uses 5 and 6 and the other 2.4 and 5.  However my iPhone is using MLO with all three channels in use.I have both the BE800 and BE655RE as my network in an Easy Mesh setup.

  @DVair  It is clear that a WiFi client would need to connect to MLO to use multiple channels.  That however is not what I'm asking about.  I am asking only about the connection between the extender and the router. I seem to remember reading somewhere that the router and the extender would utilize WiFi 7 between each other without MLO enabled.  My testing bears that out but I'm looking for confirmation. 

  @LWM It should use Wifi7 but the client will just utilize the one channel. The router/entender will transmit/receive all three channels.