It's somewhat of a specious way to rate it. It's all the individual channels added up, and some of those channels are for the Logic 7 "surround-ish" channels which never get driven anywhere close to full power. Those are some of the speakers which got left off of the vert, thus totalling a lower number. It's entirely possible that the per-speaker ratings are the same in the vert. It's unlikely, but possible that the vert uses a different, analog-input amp (like the "harman/kardon" system in the Mini Countryman, which is really a reprogrammed HiFi amp from BMW
The old Premium Sound amps were using deck-power IC amps for the outputs. The new ones are using Class D from what I hear - so they should have more power, certainly.
You're not going to find an 8.5 driver from anyone. What you're going to need is a different adapter ring (if the speaker did actually change, that is). We have a post out for local F30 owners now, and we hope to be offering validated F30 kits within 30 days.