I have a cloth top on my car as well. I have found the Porsche top shampoo to perform very well for this application. It does a very nice job cleaning, does not alter the color of the top or effect the threads.
It's a nice, mild cleaner. When washing the top, I use a completely separate bucket and a closed cell sponge. I have also found the absorber to be effective at pulling the water off of the top after washing. I do not allow it to "airdry" by itself with all of the rinse water on it, but rather dry it by hand. After the Absorber has removed 90% of the water, I finish up with a quality microfiber towel. Works great! :xyxthumbs