Is there a reason why GB doesn't advocate using pulleys to help achieve positions? Personally, I've found them helpful. Much better than bands IMO because you can use as little or as much counterbalance as you want and it is constant across your range of motion.
http://roughstrength.com/pulley-system-best-thing-happened-calisthenics/
I'm pretty sure gymnastics gyms use pulleys. But I've never heard of them used with this system.
Thoughts?