Any dictionary will show that that which can be placed before or after the thing that it is referring to.

<em>pronoun · determiner</em>

<em style="color: rgb(230, 0, 0);">pronoun · determiner</em>

Both "audience who" and "audience which" are used.

Here is a Google n-gram frequency chart.

Certain words such as group, staff, audience can be viewed as "people" or "an assembly of people." So, "people who" leads to "audience who" and "an assembly which" leads to "audience which." I personally use "audience which" but as the frequency chart shows there are many who use "audience who."