Maxwell, I haven't owned either speaker, but I don't think there is any difference in their operating principles. To the best of my knowledge, they both use a thin metal ribbon conductor on a mylar membrane operated push-pull between two rows of magnets.
I've heard some very nice speakers using the B-G driver. Unfortunately the only time I heard the Carver Amazing speaker was in a chain-store mid-fi setup, which couldn't possibly have done it justice.
I used to build speakers using ribbon drivers, and I generally agree with Tweekerman's assessment that they typically outclass cones and domes. But there are easily as many exceptions as there are rules. It's the skill of the designer that makes the most difference.
Tweekerman, I admire your enthusiasm! Did you get my e-mail inviting you to particpate in the New Orleans area audio club? Our next meeting is Friday March 1st. Within the club are several owners of speakers that use ribbon drivers. We also have a few electrostats and some exotic cones and domes, some well-executed speakers using rather conventional drivers, and at least one Altec Voice of the Theatre rig. These on-line discussions are great fun, but often the most effective writer carries the day, which may or may not correspond to which speakers really sound best (it's all tradeoffs anyway). My point is, the club offers valuable ears-on experience and a chance to mingle with kindred spirits. There is plenty of high end in New Orleans, and this is an invitation to join in. Drop me a line if you're interested. Don't worry - I don't wear my dealer hat to club meetings, nor do any of the other dealers.