jaco,

My experience with Ambi and 6/7 speakers are different. Soundstage gets a little wider, with instruments that are usually on the edge of the soundstage sometimes appearing beyond the main speakers. But what is most significant is that first reflection becomes noticable, meaning I hear the accoustic of the original recording venue more. Instead of just some ambiance extracted for the rear speakers as in a 4/5 channel setup, now the side of the hall becomes defined, not just where the side speakers are, but where the first reflection regions roughly occurs.

Ambisonic could have any number of speakers, Meridian gears are optimized for 4, 5, 6 and 7 speaker ambi setup (maybe there are others, like 1 rear surround, but I haven't configured those setup for my environment). The Aspect Ratio setting is for the sole purpose of ambisonic decoding because it has to know what signal to send to each speaker so that the resultant sound would simulate a wavefront as much as possible.

I have to admit, I didn't listen to much voice recordings, mostly just orchestral recordings from Nimbus.