Can you describe what you did when the app froze? Which version of Stage Traxx are you running and what iOS version do you have?
Check your device volume, the volume of the master equalizer and your playlist volume. These are all responsible for gain staging the Stage Traxx output. By setting master equalizer gain to +6dB you will get the same output level as in other apps with the downside that you can run into clipping problems when boosting with the eq or increasing queue or song volume above 0.