I've been told that SoundHax doesn't work 100% of the time. You may have to try launching it a few times before it actually works.
Also make sure you're using the latest version of the homebrew starter kit. It's possible you're using an old version of boot.3dsx.
Also make sure you're using the latest version of the homebrew starter kit. It's possible you're using an old version of boot.3dsx.