That's the pickle most amps can do 6 maybe 4 and thats if you can trust that number you'll be on the amps ragged edge at that point i wouldn't want to feed 3ohm speakers into an amp only states 4ohms i'd want the headroom.What you've highlighted is food for thought.
I am one of the many people, that wouldn't give much thought about the ohm's on the pretext of, most modern amps should drive the most demanding speakers, but the example you gave, regarding the B&W dropping down to 3 ohms is scary.
Thanks for that, you learn something every day
The only amps that I've come across that clearly state (and that's the important word state) they can drive 2ohm loads is naim. And for a 3 ohm dip speaker with a nominal impedance that's probably closer to 6 that's the sort of amp id want. Im sure there are many more but that one brand i know that makes a point of saying so.