I doubt Barefoot's "afoot", so to speak; he's been pretty much buried with his new speaker company for the past year or so;
You can actually set up your speakers in a 90 degree (45 degree baffles) configuration, although the wider you go away from an equilateral triangle the more chance of losing a tight center image;
One thing that might help, is to mount the Tannoy's vertical with the ports UNDER the drivers; in a soffit, you may end up plugging one or both ports anyway (one of Tannoy's ways of changing bass boost for proximity to walls) - however, if you plug just ONE port, watch for "port chuff" at higher levels due to increased velocity of air thru the port. Might be better to use a shelving filter to cut bass a bit instead.
Soffits - as I understand it, you need a minimum flat surface for at least 3 or 4 woofer diameters in ALL directions from the center of the woofer; preferably NOT exactly the same in all directions, just in case the edges of the extended baffle cause any diffraction - dissimilar dimensions would ensure that those artifacts are at different frequencies, so they should "blend" better, so to speak.
Mounting a sub in the wall makes me a bit nervous, unless you can figure a way to optimise the location BEFORE you commit; I need a lot more "cockpit time" on this one. There are some good "white papers" here, check out the bottom four on this page -
http://www.harman.com/wp/index.jsp?articleId=default
HTH... Steve