I don't have crushed granite but you might be talking about this: It's called
chat around here and its crushed limestone, gravels, and sand. It is pictured here in my isleway and I love it. It causes no problems to the feet, or mine, and I walk barefoot on it all the time, its very forgiving and has "give" and is also absorbant. I also use it for walk paths as well as 1/4" gravel and have for years. I wouldn't change a thing.
I would put it on a large area such as your 30 X 100 and I have over dirt, but your problem is that it is concrete which would requires tons and tons of it to be able to cover it over and make it thick enough to do any good.
I also have a french drain in my stalls with layers of gravels, sand, chat, but again that wouldn't work for you already having concrete.
Since 30 X 100 is in concrete and you want to use that for a barn, why not draw it up as you want it and see how much the stalls would cost you to do in rubber mats? And then just mat the ones you have to use for right now and do the others as you can. Rubber mats is your best answer to cover over concrete. I don't see a way out of it unless you go for the chat base, again, which you would need several large truck loads of it and make it very deep because it packs down to nothing fast. For instance a two foot layer done with chat would pack down to about 4-6 inches very quickly, leaving a whole lot of no drainage under it as it would hit the concrete in no time.
Another alternative would be to do the same thing with dirt, tons of dirt over the concrete, layer, layer, layer, again and again, consider it will pack down, add sand, (not masonary sand), then your bedding. From experience doing it this way requires a lot of daily grunting and crabbing when you stall clean, but I did it that way for over 30 years which explains that is why I look the way I do now, all frazzled. My face froze doing it.