You can use the Cube without the Performance Set. The cube has the
standard multisamples - sustains, stacattos, pizz, etc. You can do
pretty much anything with the Cube. The Performance set augments it,
you get the legato instruments, and runs and repitions, which make
for more realistic phrases. However, the legato tool and instruments
(especially the legato woodwinds) are amazing - the way it connects
the notes must be heard to be appreciated. You just play normally
and it switches for you to make really fluid sounding runs. This is
what sold me on VSL and I will never use standard samples after using
the Performance Legatos found in the Performance Set.
Hope that clears it up a bit. In a perfect world, buy both. But if
you have other orchestral samples, definitely check out the
Performance Set if you can only buy one. It's really revolutionary.
Oh, I'm basing this on the Giga version, the EXS isn't out for a few
weeks. Just for the record.....