I do not have a good answer for you but what you describe looks like the opposite of what happens when a player records their DP playing into their DPs internal recorder or flash drive, it sounds good as long as they play it on that DP. But, when they move that recording to another playback device, the volume is too low. This is often remedied by “normalizing” the recording.
What you described seems to be the opposite….. almost like the need to de-normalize.
I think that the recorder on many DPs has a built-in recording gain level that purposely sets the recording gain low for specific reasons. However, since you recorded your playing via VST, i suppose you may have used some sort of DAW program/app to do the recording and if so, does the app not give you a way to adjust + or - the gain level for the recording process?