Dave H - I think the Series single-coils are wound with very little wire and only work with the onboard electronics, but the other models are hum-cancellers that have normal levels of output. In this respect, something like an MXY would be a high-impedance pickup.
Because the output of an MXY, AXY, or Fatboy is fed to an onboard preamp, the output of the bass is low-impedance.
As for the Bartolini preamp... I think is should work fine with the MXYs, then it's just a question of whether you like the way they sound or not. Personally, I'm not crazy about these pre-amps, although they're very popular. You can buy an EMG AND Aguilar preamp for the cost of the Alembic electronics, so you can try out alternates without busting the bank. The big difference between the Alembic electronics and the more conventional stuff is that the Alembic has a more distinctive filter behavior than the regular treble-middle-bass of the others.
David Fung