The Grand Maestro is an incredible IEM in many ways.
The vocal boost tuning switch changes it from a mostly balanced mids/vocals recessed sound signature, to a mids/vocals forward powerhouse. The difference is anything but subtle.
The tuning modules modify the sub bass frequency by a few decibels. Changing the sub bass opens up the head stage and allows the other frequencies to “shine” through.
This is not a dedicated bass head iem. The bass is excellent, but it doesn’t overpower. This is an IEM capable of presenting music clearly and concisely throughout the frequency range.
Grand Maestro has the best head stage I have experienced on any IEM to date. Width, height, and depth are excellent on all three axis, and, instruments, vocalists, sound effects, etc. present from all 3 dimensions of the stage.
Thus IEM is worthy of consideration.