Just mounted my AS-B2's this weeked
I used the BT-77 mount, it's a quality mount made of almost all metal, can hold a 55 lb. speaker, but it only swiveles up / down 7 degrees, you need to consider this. You can move it side to side all you want, only the tilt is limited. The say screw it in if you are tilting it down but I did not, it uses a large screw for a "worm gear" allowing you to tighten it down really good. Do a search, I got mine for $59, that was a cheap as I found it for.
The other mount was hard to find and it appears to grab the front and back of the speaker vs. the sides like the B-77, I think it's used for side-wall mounting only. I was quoted $40 to $79 for this mount; if you get it let us know how it works out.