error on union of bpc cube and bw cube

hi gurus:

Hope this is the best room for this topic.

I d like to ask about the best option to make an union of BPC cube and BW cube, since I m using BW 7.4 I tried to use a composite provider but it show the next error: "The data types for field Amount of the CompositeProvider do not agree", since 0AMOUNT is CURR data type and SIGNDATA is a DEC data type.

I thought about using a virtual provider (module function) but I ve heard it has performance issues.

PS. the bw data will not be loaded to bpc and bpc data will not be retracted to bw.

regards

mah