Sound personalization is an important developmental step. Every hearing is different and changes in the course of life. Acoustic filters are just the beginning. With the adaptation to your hearing, it is already possible to adjust the sound. The perfect sound out of the box for everyone will not exist in the future either. After the first impressions I probably prefer the A2O also because I already own a closed headphone with the Campfire Cascade. The Cascade is in contrast to the A2C easy to drive.