Lower sensitivity and plays louder?

Ok so I got a 30 or 35 watt per channel rotel integrated a week or so ago. When i got it I hooked it up to a pair of Energy towers rated at 91db. Had to crank the amp well over halfway to get to normal listening level.Then my B&W dm303's showed up, hooked em up and get the same volume with the control well under halfway!!! What gives? In my towers there are 4 midrange drivers each and a tweet, the BW's are 2 ways so maybe thats the reason but i really dont think so.
B&W is going to be very conservative in their specs and they are probably rated at 8 ohms (an easier load to drive). I do not know the impedence rating for the Energy but they probably only give a nominal impedance and it could have some frequencies that have considerably lower impedance which makes for a more difficult load for the amplifier.
It may also be a difference in dispersion and one speaker filled in a relative null at your seating position.

You'd have to measure the voltage at the speakers and measure the SPL in the room to really know whether the sensitivity specs are accurate. It's not uncommon to see in Stereophile speaker measurements that the sensitivity varies from the spec by a couple of dB.

It's very difficult for a speaker manufacturer to obtain consistency across a speaker model -- too many variations in shipping lots of drivers and crossover parts.