Diffusers on the front wall would still be for "live front". Diffusers don't deaden sound, they just make it more diffuse (break up the reflection to cause less interference with the direct arriving wave at the listener).
Front-firing speakers
(except for maybe horns) don't radiate only toward the front. The *desired* wave is only forward, but there is still plenty going toward the sides and to their back, just aim a speaker away from you and see how loud it still sounds! The higher frequencies are less toward the back, though, and unfortunately the lower frequencies are much less easily diffused (or even absorbed, for that matter) than the highs.
But a dipole speaker (most ESLs, Magnepans, Apogees, Linkwitz, etc) radiate the same toward their back as toward their front. It is a good idea to deal with the back wave, either break it up with diffusers (if you want to keep the room sound lively) or absorb it (if you're ok with some deadening, or want an easier route than constructing diffusers).
