The drop in volume to 80 is built in DPS 1.x to address some laptop systems having distortion when volume was set to 100. This is a legacy problem now.
Please try these tests with DPS 2.0. There are settings available to disable all automatic volume adjustments as well as significant improvements in audio processing and handling. We are focusing on making all changes in DPS 2.0 to replace DPS 1.2.4.