I use an artificial sheep fur mit with Zymol car wash. After the is dry I remove any type of lint with a regular lint roller. About once a month, I spray with Ragg Top protectant. That process work well for 5 years on my 2012 Boxster.
I would not use a brush to scrub it. I have used a vacuum cleaner brush attachment to vacuum the tops. Annually I use something like 303 fabric guard to keep it water repellent. If the top gets wet while rinsing the car I lightly blot the water off with a towel. The last thing you want to do to the top is abrade the fabric threads.Boxster owners: what sort of brush do you use/recommend to clean the soft top?