Viridian:
I think that you missed my point. I suggested making a distinction between cross over efforts and collaborations. A cross over would be a change in genre ... Placido Domingo, an opera star, singing songs from the great American songbook (it really merits a listen). A collaboration is not a change in genre, per se, but rather presenting material in a different way. For example, Elton John's music is normally not accompanied by a symphonic orchestra. Additionally, it's hard to criticize Elton John for not writing a symphony, when a symphonic orchestra doesn't write one either.
Regards, Rich