Sorry for late update. I've tested the Volume levels with and without the ACM using different Headphone Gains. And it's true that you have to turn the volume on the ACM almost to max to get it to equal the volume without the ACM using Headphone Gain between 16-31 ohm (low). Using Headphone Gain of "High" would require you to lower the volume of the ACM. Which isn't needed. Just leave the ACM at 90%+ and call it a day with Headphone Gain at Low as it's just as good IMO.