I think I am right in saying they Asus call it "Stability Adjustment".
It's found under Administration / DSL Settings / Stability Adjustment (ADSL) and goes from 5db to -10db. The DSL-AC68 definitely supports it. Probably some of the others as well.
Can any one recommend the DSL-N55U to replace a Billion 7800 wired and HH3 wireless access point. I know bit cobbled together but the Home Hub has served well but I have a problem with single thread downloads pausing but multiple threads are fine.