I know that the Paraliminals are now built to contain Holosync technology produced by Centerpointe. For their meditation based upon Holosyn they recommend a type of headphones which have the widest possible frequency response (6 Hz - 23000 kHz). Although we do not hear below a certain frequency, the binaural stimulation still takes place and has an effect on the person. For the initial level of Holosync there is not specification about the headphones, but as soon as the person gets into the personalised levels, headphones do matter alot.
Upon their recommendation I bought the MDR-EX71SL, which are Sony's first closed type FontopiaŽ Design Bud Style Headphones. This is what they say about them: hear the powerful, resonant bass response. Additional features include a Super-light In-the-Ear Design, New, Super-Small 9 mm Drivers which are ultra-compact drivers that produce powerful sound with space left over for the sonic isolation of our newly-designed Soft Silicon Earbuds. Two Sizes of Earbuds that accommodate a full range of ears, a 400 kJ/m? a Ultra-High-Power Neodymium Magnet, a Hard Carrying Case, and Earbud Holder are also supplied.
The cost for such high quality device is only US$40 or so. This is a real bargain. Although the quality of the sound is excellent, they break easily (the plastic cover comes off at the attachment to the ear bud and uncovers the wire... i had mine replaced a few times by Sony under warranty). Go to Amazon for problems encountered by people. Here in Australia, it appears Sony has withdrawn the product from the market. They have replace it with a white equivalent, which is not yet available.
Maybe Alex can comment on the headphone requirements related to the Paraliminals. I think that ear bud models are much preferred to others since some of the Paraliminal tracks can be listened to while asleep.