I got myself a pair of the Monoprice speaker brackets earlier this year, but not for use with my Axioms. They are made from fairly heavy gauge steel plate and are quite sturdy. Each bracket weighs about 450g (one pound). The bracket not only allows the angle between the two arms to be adjusted using the wing nut shown in the picture, but also allows the smaller plate to be rotated on its axis - something that's not evident from the Monoprice picture.
In order to fix the QS8 to the bracket, you would need to use a single bolt that would go into a threaded insert that's at the back of the QS8 (see the QS8 owner's manual). The smaller plate of the bracket - the one that's supposed to be fixed to the speaker, has a hole about 4 mm diameter that might be too small for the size of bolt that you're supposed to use with the QS8. The larger plate that's supposed to be fixed to the wall/ceiling does have a hole that would be OK. With some improvisation, you might be able to make it work.
The dimensions from the packaging are below.
[Edit] Sorry, the image doesn't work too well. The larger plate is 100mm (3.9") x 100mm (3.9"), the smaller plate is 40mm (1.5") x 80mm (3.1"). At the angle shown, the distance from the wall to the centre of the smaller plate is 145mm (5.7").