Yes, I am (Thanks!) combing through what's on the web, chunk by chunk, though I haven't seen too much, other than broad groups of frequency -related definitions (Alpha, Beta, Delta, Theta, Gamma). There ARE some interesting claims and loose facts out there and I have yet to marshall them all.
But here, for instance, with the "brainwave generator" (anyone can google that up and down load it for free... it is share-ware with an available pay-ware upgrade) I configure a BFO to go gradually from 20 to zero. As I listen and 'feel' the sound, I can see exactly at what Hertz the thing is cooking at. And what I observe is that the feel of each BFO is somewhat distinct, that some have a much stronger 'feel' than others, and that their relative placement in the number-scale, or spectrum, if you like, seems greatly, or even entirely, independent of the 'feel' that they produce. For just one example, 19.5 hz. BFO has a substance to it that is not present at either 19.3, nor 19.7. Similar, though different, experiential anomalies occur at other particular frequencies. Some of these may be artifacts of anything in the structure of the sound production/perception system (for examples, a certain chunk of transistor may 'ring' at certain frequencies, earphones may do the same at others, ears, ear canals, yada yada...).
For those interested in following, it is not hard to set it up so that over ten minutes time the BFO goes from 50 to zero. For me the effect as I listen is like descending though levels of varyingly dense atmosphere, which are not at all successive in their concentrations. (Sorry, it is hard to describe... I know there is a better metaphor for the experience but it has yet to surface.... something like the different colors one sees on a spinning top as it gradually slows.... but then who knows what a spinning top is these days? Much less having experienced the thing?) An odd after effect is, that when I stop listening to the BFO experiments, and pull off the head phones, for a time, generally a few seconds, all regular sound has a very difficult to describe quality.... it is as if each independent sound occurs individually inside its own mecurical sphere, like a bubble, and it then has an almost xylophonic 'aura'. Gah. I KNOW that sounds weird, but it is not easy to describe.
Anyway, it seems like an interesting thing to explore.