Rick, you're probably referring to our discussion of bridging that took place about three years ago
here , and especially to secs. 3.5.3 and 3.5.4 of the linked article.
Slack, I wasn't going to bother discussing the point since you seemed to have lost interest in bridging(which in contrast to the form of "biamping" that you're discussing actually does increase the power available to the speaker), but you might read the sections of the article mentioned. The short version is that the impedance of a speaker can't change(e.g., from 6 to 3 ohms)when the amplifier driving it is bridged, but the amplifier is putting double the voltage(theoretically)into the speaker, and because of Ohm's Law(I=E/R), when the voltage is doubled so is the current, with impedance staying the same. So, the amplifier has to put out more current because of the increased voltage, but this has nothing to do with the impedance of the speaker. The amplifier doesn't "see" a lowered speaker impedance because it can't see something that isn't there.
