Headphone playback with ultra linear response

I am looking for a headphone system (including headphone amp, CD player) with straight linear frequency response to use with my Centerpointe program CD. The Centerpointe is a personal development program which applies audio signals aiming at brainwave stimulation and synchronization for various benefits. You can go to their website www.centerpointe.com if interested. The program goes in levels and as one progress the CD are encoded with lower carrier frequency which is the precise sine wave tones to stimulate the slower brain wave patterns, and bring about deeper level of positive change.

I am currently using a Song portable CD diskman and headphone to work with these, which is fine enough and cost effective, but as I am getting to the point when I want greater benefits and willing to spend more to achieve that. I would like a better system that can accurately reproduce all the frequencies encoded in the Centerpointe CDs. As such, I am not looking for good sound as such but highly accurate frequency response. Any recommendation will be appreciated.