John is correct - you need a pair of BL150 amps plus the displays & wiring. In all honesty it will end up much cheaper & easier to simply buy a pair of Beolab Penta's - even if this means selling your Beovox's to fund this. The BL150 amps are the first ones used in the Lab penta range & were replaced with the BL200's & they are now starting to develop problems of their own.
The only way it would make sense to buy the parts & upgrade a pair of Beovoxes is if they were in truly mint condition or if they had some sentimental value.
Chris.
The use of metaphors should be avoided like the plague. They're like a red rag to a bull to me.