Drywall anchors will work, especially if you use one for every hole on the bracket. Which is overkill. But overkill with non-stud mounted hardware is what you want.
For non-maximum but still effective overkill, I'd put toggle bolts in the left, middle, and right horizontal holes, then e-z anchors in the rest.
Ditto.
Although I've never used toggle bolts I used the appropriate sized E-Z anchors for every mounting hole in the 'T' bracket with rock solid results. Our four QS8s have been hanging on the walls for five years and every one of the brackets are mounted with only the E-Z anchors.
