"as wide an audience as possible" is correct and usable in written English. It is used when you want to emphasize that an action should be directed toward a large number of people. For example: "We want to reach as wide an audience as possible with our new product launch.".
Her riposte to some of the nonsense it contained is so devastating that I simply reproduce it here (because it deserves as wide an audience as possible): This is possibly not a national talking point, but, damn it, it should be.
Send your 'ethical' message out to as wide an audience as possible.
"They want it to speak to as wide an audience as possible".
It's often said of documentaries that they deserve to have as wide an audience as possible.
Moving forward, she wants to address as wide an audience as possible.
He stresses that he is keen for his VR films to reach as wide an audience as possible.
For Jenkins, this makes bringing a character such as Chiron to as wide an audience as possible yet more crucial.
Being a terminologist, I care about word choice. Ludwig simply helps me pick the best words for any translation. Five stars!
Maria Pia Montoro
Terminologist and Q/A Analyst @ Translation Centre for the Bodies of the European Union