Turn up iPad volume either up to 100% or as much as possible without triggering the iOS hearing protection.
Stage Traxx uses an internal safety margin of 6dB. This means that you can boost volume within Stage Traxx up to 6 dB without having to fear distortion. Keep in mind that if your playlist/queue volume is set to +6dB, this safety margin is used up. If you now play a song that also has a volume boost, you can get digital distortion.
Apart from this, I would recommend staying near 0dB except for background music playlists.