I find that the optimum level for listening is about a tenth of a twist higher than the level at which I worry that it is going to bother the people in neighboring apartments. I do believe there is a minimum level that you must have to get the full benefit of your system. Paul McGowan of PS Audio has done a number of enlightening YouTube clips on this subject:
https://www.youtube.com/results?search_query=PS+audio+low+level
https://www.youtube.com/results?search_query=PS+audio+low+level