Guys, I've just replaced my HH5 (and HH6) with an Asus DSL-AC68U and I let it do an auto setup, which has resulted in a fast and stable connection...actually gained some connection speed in both directions over the home hubs.
Looking at the settings, the only thing I'm tempted to tweak is the 'Annex Mode'. Via the auto setup it chose 'Annex A/I/J/L/M', and in the DSL Log I can see it reporting 'Annex A'. I thought Infinity2 is Annex B......do you think I should switch to this in DSL Setting menu? I don't know whether the different annex mode settings simply either work or don't work, or whether selecting the correct one might optimise performance.
I'm running a TP-Link VR600 rather than an Asus router but mine is set to VDSL2, Annex A/L, and is working fine. I think you can stick with auto setup.
Ignore the Annex setting on VDSL - changing it on the AC68U router will have no effect to your connection (I've tried changing it).