There is no encap brush attachment for the Challenger - that I know of. Excellent-Supply's FiberPlus pads work very well for encapping with the velcro face of the Challenger's pad driver. I alway also have on hand a couple of E-S's FiberMax pads, for really cruddy commercial carpeting.
They are more coarse and more aggressive.
Mark, the brush i was talking about is on smart cleaning solutions.com sold as an encap brush.
Also, I've been using ccs abstration vlm and tlc for years and wondered what you guys use. Any input is always appreciated, thanks.