SmoothSound,

Ambisonic was designed so that the recorded information could be played back so that the original ITD cues are preserved, no matter what speaker layout you have. It in effect attempts to recreate the original wavefront from every sound source that was at the original recording.

If you have an Ambisonic encoded disc, you could play it back and swap between 4 and 5 speaker output, effectively allowing it to attempt wavefront reproduction with the front 2 speakers instead of 3 (it also does it with front/rear, but you are keeping those variables constant).