Hi Glorious and welcome to the forum
I'm not sure of the technicalities, so I would think you'd probably get a better answer of the support team (perhaps using the Contact Us link at the bottom) or posting in the
Having Problems? - Project Meditation Community Forum forum.
Typically, to the best of my knowledge, most headphones will work ok, providing they allow the sound to be produced as it is on the CD/MP3 without altering the bass/treble automatically (some have built in graphic equalizers or special "modes" for different types of soundtracks).
The frequencies of the binaural beats are generated by a very slight difference in the sounds produced from the left and right speakers (frequency phase difference), so the headphones do not have to be actually capable of producing those frequencies directly themselves, as the brain combines the different higher frequencies received in each ear to generate the binaural frequency.
Hope that helps.