I'm familiar with this atheists standard notion. It is just an assertion. Even if we would be able to explain the whole universe it would not explain away God. Just because one can explain the whole car in terms of mechanics it doesn't follow that he has explained away Henry Ford. That's an error in reasoning and, as I believe, a display of the suppression of truth as I mentioned.
Indeed, God is the necessary foundation of all knowledge and explanations. Without him there is no basis for truth, knowledge, logic, morals or uniformity of nature. What is your ground for these without God, that is to say in a universe made up only of physical entities?