I can offer a hypothetical--however do not know know practical it will turn out to be. There is a fair amonut of bad science on this topic on you tube. The gamma wave frequency is associated with attentional focus and arguably a unified sense of self. If it could be entrained it should lead to a meditative focus-like exceptionally well-trained meditators. Some but not all studies on meditating Buddhist monks suggest this is so. Does this really and more generally occur--I will say there is nothing lost in trying--we all go into a 40Hz range on occasion without ill effect-- but I would not put confidence in the purported methods out there at present. Good luck.
Theta waves have another interesting characteristic. The Earth has a measurable resonance of 7.83 hertz known as the Schumann resonance. Because the Schumann resonance is a constant background frequency surrounding all life, it may play a special role in biological activity. The Schumann resonance frequency falls within the range of theta brainwaves and may have something to do with why these brainwave frequencies are so powerful. 
This session uses a proven technique for inducing deep relaxation, playing one frequency for two minutes, then alternating to a second after a 30-second ramp, then reversing the process. The first half of the session switches between a serotonin-boosting 10Hz and the grounding and rejuvenating 7.83Hz Schumann resonance. The second half of the session goes even deeper, alternating between the relaxing 7.83Hz and 6.3Hz, a frequency associated with releasing anger and irritability. The session ends on a chilled out 10Hz.