Soffit mouting techniques

I 've got a dilemna about soffit mouting my monitors. First of all, let's describe the situation: I bought a house with a garage in the garden, and i will use that place for building my recording studio.In that garage, previous owner intended to build a recording studio also, so in the main room, there are 2 empty spaces built inside the concrete wall yet, originally intended to put monitors in it. I also read a few weeks ago, an article on some forums, about soffit mounting articles, and this article explained that the best way to flush mount monitors, would be to have a dedicated placement inside a (concrete) real Wall, i mean not inside the extra acoustic wall that can be built on it, but inside the original one. 1) I primarly put a post about that question under Ethan Winer forum , then SWL and Scott Griffin helped me with some good explanations: They told me that concrete is very good for absorbing vibrations that would come from the base connection of the monitor, anyway concrete is better for that, than any plasterboard, or any other mouting system.Then, the monitor would have to sit inside the concrete 'box', then get a good absorption wall built around, and a bezel as a mask, without edges touching the monitor... 2) Given all these suggestions, i would go direct and use these 'boxes' for my monitors, but the pb for me is that the space behind in the next room, is eaten by this box space, reducing its chance to become a post production room.Furthermore, i would have loved to transform later this big space, into a live recording room, instead of a Control room (ceiling height is 13.4' there !) So I thought about an alternative: I may destroy the empty boxes, fill the space with concrete, and fix a horizontal stand to the concrete wall, put the monitor on it, and then build absorption all around, etc...in a way that monitor vibration would only go to the concrete.Then, i would destroy the boxes without any regret. But before doing anything, i have to be sure not to forget any good reasons for keeping that installation intact...And my feeling is that my skills there, are still limited. Finally, depending on the suggestions, i will decide if i use that room for a recording live room, or for a control room, which is an important decision to make, from the beginning. The first version of the studio (the empty concrete boxes are in the 'control room'): After modification (if i destroy the box empty space in the concrete):

Well, it seems there's no reactions to that post...Should i deduce nobody around has got any experiences in soffit mouting monitors? I had just been advised to post at John Sayer forum, which is said to be technically helpful...

do a quick search on "soffit mount speaker" and you'll find plenty of information on this topic. 8) i think your second design is better but you could use those existing spaces to be traps since you'll need them anyways.