What does the playwright of Amadeus try to get across to the audience?

I think that Shaffer accomplishes his end goal in bringing
out a complexity and depth to both principals in the work.  The audience is left to
muddle through the newly established intricacy of both Mozart and Salieri.  Mozart can
be still seen as a musical genius and pioneer, but there is more to him after Shaffer's
depiction is complete.  One sees him in a sad and almost tragic light.  The fame and
praise that is worthy of him is something he never fully appreciates.  His genius is
stunted by the social blight he received and also brought upon himself.  Mozart is
revealed to be as complex as one of his own musical masterpieces where there is more
than one element being pursued.  At the same time, Salieri is seen as more than simply
"good" or "bad."  One sees him as one driven to do terrible things out of a source of
goodness.  Salieri's evil ends is motivated by a worship of music, a love of God, and a
desire to be the best.  In each of these lies virtuous actions, and yet, all three
collude to drive Salieri to destroy Mozart.  It is here where Schaffer makes it very
clear that there can be a distinct difference between human being and artist and we, as
the audience, are left to sort out which has or holds more
value.