Dan, I originally had AXY's in my BigRedBass. They were just fine, but exceptionally transparent. I rolled the dice and changed out to FatBoys (thanks to Mica and Bob Novy). It's not a night+day difference, but I prefer the FatBoys for me. If it still had the AXY's, I'd be just fine, but since I had a choice, I went with the FatBoys. Since Alembic tends to put the bridge pickup right next to the bridge, using a FatBoy only at the bridge works for some guys to buy a little thicker sound from a thinner spot.
My best analogy would be that the AXY's sound like very good reference studio monitors or a very good studio mic, whereas the FatBoys are still very accurate, but with just a bit more coloration, as if you're now listening to the playback on exceptionally good home speakers, or mic'd up with an SM57.
J o e y