the program actually achieves volume adjustment by adjusting my system volume
This is very odd as I've NEVER had MPC adjust the system volume. It's always adjusted its own internal volume.
Under View, Options, Playback, Output, Audio Renderer: Change it to System Default and see if that solves things.
I am not familiar with how MPC work internally, but isn't it suppose to not tuning my system volume levels for whatever audio render choice I made?
In fact, my PC has onboard audio and a Creative Sound card both active and each takes care of their own speaker set. One of the set of speaker I only switch on while watching DTS movies wherelse the other set of speaker is my day to day use PC audio output. So, as you can see, if I stick to MPC as my player, my Audio Render can not be a fix one, I need to switch it between my movie watching session and normal PC working session.
I have just solved the above problem:
I create an AutoIt (script base) exe which always adjust back my Wav level to 65%, I then have MacroExpress auto run the exe every time MPC is closing.
Just to share my experience in MacroExpress with everyone here: I have been a user of MacroExpress for many years, recently I have upgraded to its PRO version. It has features to adjust most of the system volume except for Wav... Sarcastically, I have to resort to a freeware scripting program...
I dislike MacroExpress Pro's way of accepting user suggestion and dislike very very much their hostile user forum.