Well, as I see it, reading it to the letter you'd have to run 1- 15A circuit to cover your 2-6A openers, and then one each for you other 8A openers, totaling 4-15A circuits.
Now personally, considering this is a 'residential' or 'personal non-commercial' home garage, and seeing that the chances of more than one opener wld be in use at the same time, I'd have no problem myself running only 1 circuit for all. OR 2 circuits and config them as one for the 6A 6A 8A, and one for the other 8A 8A. OR better yet, 1-15A for a 6A & 8A opener, 1-15A for another 6A & 8A opener, and 1-15A for your last 8A opener, totaling 3-15A circuits.
But in the end your really only saving one or two extra runs to conform properly and only you know your or your customers intent of use, so follow your gut feeling and do as you feel comfortable doing.