Hello Prasad,
and another welcome to the forum.
The MXY56 is an Alembic MXY low impedance pickup long enough to correctly voice a 5 or 6 string bass (the original MXY was designed for a 4 string setup).
PVF refers to the active onboard electronics: Pan, Volume, & (low-pass) Filter.
PVF-2 adds a Q switch which gives a boost at the low pass frequency selected with the filter knob (rotating the filter with the Q switch on sounds like using a Wah pedal to shape your tone).
AE-2 is identical to PVF-2 except there is no pan knob, so it's usable on single pickup instruments or instruments with a pickup selector switch.
AE-3 substitutes separate active (cut and boost capable) bass and treble knobs in place of the filter knob.
All of the PVF and AE types require an internal 9 volt battery in the instrument to boost the pickup(s) to standard instrument level.
The 3 way bass and treble switches are an additional tone option routinely found on Distillate, Europa, and Rouge models. Contact Alembic regarding pricing for that option.
I hope this helps.
Mike
