Hi,

I am thinking about rebuilding a Beovox Cona passive sub to an active one by adding a SUB amplifier.  Has anyone done something like that or have some experience?

This rang a bell! Look here. Not sure what happened, but sounded interesting!

Check out eD audio

http://www.edesignaudio.com/

Their sub amps are made by Keiga, with B&O ICE technology.

I have the model LT1300 in my sub, but you'd probably want a smaller model for yours.

Stay away from those with Switching Power supplies - pure headaches. You want a nice fat toroid transformer with big fat power capacitors.

Also, don't expect a long lifetime from amps with BASH technology.  I'll get my flameproof suit now!!! This was learnt by hard and costly experience. BASH is cheap for the manufacturers, and not relevant for those who replace away their electronics every year.

Menahem