Well, I brought the PSB Alpha B1s home this evening, and I'm playing them now. Without getting into sonic detail, my "bottom-line, first impression" summary is this: They sound like they are a little smaller with similar quality, and, well, that's what they are. Ha. They sound about as good as I would expect smaller, less expensive ADS speakers to sound (different, but as good). So I wouldn't consider it a lateral move, but still a good move for downsizing.
They do sound better than I expected, notwithstanding all of the good reviews and my curiosity. I wasn't expecting quite the presence of the bass that they have (I do run a sub, so perhaps it's not as noticeable). It's not quite as tight (probably for being ported), and they don't seem to push quite the same volume before breaking down. But in this small room they don't sound anemic in the low end.
I generally listen with the tone defeat on (that's just a personal requirement I have for speakers, that they sound good enough on their own). The sound isn't quite as full or bright as the ADS, but they seem to produce more tonal accuracy in the mid-range, with more subtle, yet very clear highs. So they have more of a warm sound with a little less overall presence. An overall very pleasing sound that I could live with, I think. The size is really perfect.
That said, I have 4 days to decide, and the speakers have not been broken in as yet.