Hello Richard, no doubt if you've been to Johns, you recieved good advice. However I have a few offerings for you. It is very easy to draw well intentioned ideas without realizing the reality of space. Like walls, which IF you plan on building a two leaf iso system, require a REAL wall, not a line on a drawing, and space they occupy in reality, alter the percieved limits of whats REALLY going to happen when you build. Take a look a these drawings. I traced your "lines" and put them into real quantities of floor and corner space. Look at the difference a few REAL inchs will do to your monitor vectors. I'm no expert on placement issues, but most professionals agree that a 30 degree orientation from the monitor centerline works well, and that being said, they also agree the stereo monitor junction center lines should be about 18" behind your head at the engineering position. Look at the difference a few inchs of wall space makes especially in a situation like is shown here. The corner of the existing walls, what ever they are, makes for a very difficult speaker location. Idealy, if you are planning on soffet mounting, the speakers would actually work better right behind that corner, but that not being probable, will either have to be forward of it, or back in the area shown by a red speaker box. That foreshortens the stereo vector lines. I have drawn them as though they are mounted like barefoot suggests behind an extended baffle, which is within the iso wall boundarys, NOT through them, as any penetrations in the iso wall negates the purpose.
So, I would suggest you draw with reality in mind, TO SCALE, otherwise you are spittin in the wind. Push comes to shove at building time, and reality ALWAYS wins. Anyway, thats my advice....draw EVERYTHING as if you were depending on it to MAKE IT REAL. Cause, thats exactly the point. I'm not here to critique your plan, only offer a hint to prevent ....OH SHIT< IT WON"T FIT!! experiences later. I've seen it happen so many times I couldn't count them. People just don't take dimensional reality into consideration in planning. A line here, a line there, and it looks great on paper. But make a wall if fit in the width of a line in physical space,
and your fooling yourself. Well, thats my .02 anyway. Good luck.
fitZ