A two way speaker has typcially a woofer, for low frequences and a tweeter or horn for high frequences. In most cases, this is typically used in vocal reproduction and since most keyboard amps have used two way systems to get a nice clean and clear sound, this has been the standard practice. Most home hi fi quality speakers have used 3 way systems to get the best, mosts natural sound for prerecorded music where you are not trying to drive a lot of volume out to an audience and rather have a smaller area here a more natural sound. The use of tweeters in home equipment rather than a horn, which carries the sound out farther but with a harsher tone was what has been mostly used in 3 way loudspeakers sold by most companies. What Yamaha has done with the AS312 was to still use a large diaphram horn, but reduce it's size, thus not giving such a harsh sound as most large diaphram horns put out. The use of the midrange speaker definately improves the middle frequences and makes keyboards, CD's, MP3's sound more natural without a harsher tone usually attributed to 2 way speaker systems which never have a mid range woofer.
I'm not at my store right now to give the weight but my guess is about 30 lbs. each.
The vocal harmonizer effect in the Behringer is a fixed interval which moves with you as you sing. Again, not being at my store, I don't remember if it is 2 part or 3 part but it is a nice effect for something just part of this inexpensive mixer/amp. There are no editing functions in the mixer but Behringer does sell a single rack pro effects processor which is completely user programable and sells for $149.00.

George Kaye
Kaye's Music Scene
Reseda, California