I know, I know. I could just buy Late Night. I just find it irritating to have all the other stuff that goes along with Late Night when the only reason I would have got it in the first place was so my sims could play piano.
Has anyone been able to make the instruments and instrument skills base game compatible or is this a stretch of legalities and such?

I'm going to have to vote for the stretch of legalities thing on this one. The developer's jail sentence likely won't be very long, and they will occasionally get to play the piano while they are in there, but probably not really worth it.

Or a more succinct way to put it would be no sorry, you can't do that.

thanks for replying. I guess I'll just have to live without the bass until I can be bothered to fork out for Late Night.