Groups of sixes in a triplet feel should feel and sound rather natural due to it being a mutiple of three. The lick itself is a tad tricky due to the quick "back and forth" motion, but keep in mind that we're descending from the highest note/descending 6, second highest note/descending 6, third highest note/descending 6, etc.)
Much like fives, odd number groupings will always cause some trouble. Sevens are no exception. Play slow, get a feel for what each grouping has in common and how things fall beneath your fingers.
Nine, another multiple of three will also sound rather natural when you get into the swing of things. It is, however, another great method of adding some excitement to your lines.
That's it for this month, folks! Happy shredding!