actually, just thinking, and I want to you take this as it's meant - Ie concern. If you think the iphone 6 is too quiet and you want things to boost the sound and bass, it honestly sounds as though you may have already damaged your hearing from listening to stuff on headphones for too long at too high volumes. I've heard an iphone 6 at full volume, it's quite loud, even with the eu limiter on it.
So, as a note of concern, please take care!