Sometimes you learn things after the fact supporting multiple corrolaries of Murphy's Law. I believe that I might have really stepped into it and hopefully, it is addressable.
I have a pair of beautifully sounding (to my ears as well as having the WAF) a pair of 604s (series 3) for the past three years. They are wonderfully matched to an LCR 600 center channel. While these are not in the 800 series, for us they are fabulous.

And for me, they have made listening to both music and using as a home theatre set up (mated with a Hsu STF-3 sub and a pair of rear placed surround speakers) the delight of my daily listening experience.
Recently took the plunge, and bought our 1st large screen plasma (50") to enhance the pleasure, which resulted in a redesigning of our family room. The end result of purchasing + to keep the plasma + the WAF =the redesign which included the creation of an entertainment center wall unit being built to house it all.
The design included having the 604s placed into surrounding enclosures in the EC (entertainment center) that will have approximately 1.5" on either side & above (with about 2-3" behind). The center channel will be in a similar situation being placed on a bookshelf like setting above the plasma. Esthetically it is visually lovely since there will now also be a caticorner gas fireplace (floor to ceiling unit) to the left of the EC, thus completing the entire length of the wall where the EC is. Visually Lovely, However...
After construction began, I realized that placing the speakers in the EC might impact on their sound. Naively believing that since the speakers were enclosed without baffles that everything would be ok. (The CC has a baffle which will be closed.) BOY, was I mistaken as I was correct about the changed impact since reading this thread helped me to realize that the sound will change if the 604s are elevated, placed near a wall, near other objects, etc. So I placed my head inside of the proposed enclosure and noted the echo as I spoke

The unit is about 90% done (being constructed in my den) and changing the size/locations are not discussable as per WAF. In otherwords, I should have thought about this before the design and construction. So be it. Now, I must find a way to somewhat address/correct it.
Other factors involved:
-Changing speaker locations are out of the question.
-Excellent planning for speaker wire channels have been effectuated using pvc pipes behind the unit so that ample-hidden slack can be achieved.
I have considered several options:
1. Placing the 604s on a pull out (if I can construct one) so that when in use they are somewhat in an open setting. (However, the right front when pulled out, would also be about 4" off of the side wall of the room).
2. Placing closed cell foam/insulation in the rear of both cabinets (and linked to the speakers) to assist in reducing the potential rear echo when the speakers are moved out on the tray
3. Visiting a furniture reupholstery store and obtaining closed cell foam (used in cushions) and wrapping them in a black speaker cloth and placing them in the open portions (left/right/top/back) of the cabinets which measure approx 1.5" all around the speakers and leaving them intact.
BTW- where would I be able to obtain black speaker cloth to cover the closed cell foam?
While I am open for suggestions/comments and the like (other than being bashed for this error on my part, which I admit was a biggggggggie), I realize that there might not be much that can be done. However, with the great minds and wealth of experiences that are out there, one never knows unless I ask.
Thanks in advance.
..Mark