This appears to be a built in feature, i don't understand the purpose of it though, DAC still uses the brake, that sort of defies the point, one uses low range downhill to avoid using the brakes as they may overheat, if we engage DAC, we are still using the brake... thats just stupid....
If you have the space, use it practically, put the vehicle in low range, slip the lever to manual mode, and go down a hill without DAC, then repeat this procedure with DAC, shouldn't be much difference