With regards to bring any 5.1 bookshelf system into 7.1- I always consider that more channels and speakers are best ONLY if they can be properly selected and placed fairly closely to THX recommendations. This would involve using some type of diffuse wide dispersion speaker on the side walls and possibly on the rear wall also.
For most users this would involve adding something like the C-R100 to the side walls to provide the necessary dispersion. Use your existing surround speakers for the rear ch 6&7, where a more directional speaker is called for.
I'll have to do some checking on the bracket question. We'll see if there is a pattern. I've not heard many, if any, problems with them.
Michael