Excel Median with nested if statement with wildcards

I'm trying to build dashboards for my co's support team. I can calculate average response times (i have four times i need to take an average & median) with a pivot table but median has to be formula-based. To make things easier, I want the support manager to be able to search by three parameters - Agent Name, Category, Priority. All the data is in my 'select data' tab and the formula i have is:

{=MEDIAN(IF($B$2='select data'!$E:$E,IF($C$2='select data'!$F:$F,IF($D$2='select data'!$K:$K,'select data'!S:S))))}

b2=agent name, c2=category, d2=priority

I'm using a drop down menu for the three categories and when i select a specific agent, category or priority, it spits out the result i need. When i try to use * or "*" in the drop down to capture all agents/categories/priorities, the formula spits out a #num error.

I would love some help on this.