With the way the engine works and TB works when it comes to sound files, .wav format is the most reliable when it comes to functioning within the game. When it comes to things like bit rate, and depth it just flows better in .wav Better with the short bursts that FX and Kiai's deal with.
You may also notice the BGM's and FX are also either in .wav or .ogg and there are reasons for that.
Buttttttttttttt .wav files are larger. Considerably. Dunno if anything would want to be implemented to satisfy the needs you are looking for but it is not impossible. Changes may/probably would need to be taken into account to fix any underlying issues that would most likely occur from a different file format.
Because I don't know if you look at the Support Thread, but every few days there is someone with a Kiai issue. And if it is not fixed via Custom Folder reset then its usually something to do with the file itself, which could have quite a few variables.
Something to think about.