IMHO, the DynaQuad/Hafler passive speaker matrix surround sound "decoder" sounds best with stereo content (better that Dolby Pro-Logic 2 music mode).
There's somewhat of a surround sound playback infrastructure (may be soundbars, but it is there), radio can take advantage of it by broadcasting matrix encoded surround sound downmixed from surround sound master recordings - it's close to a free lunch for radio, they just play the stereo matrix encoded quad content, no new broadcasting equip is needed.
Kirk Bayne