Chart with Dropdown selections

So, yes, you can do this with the Disconnected Table Trick. In general, to use a measure in that way, you need to use the Disconnected Table Trick as this article demonstrates: https://community.powerbi.com/t5/Community-Blog/Solving-Attendance-with-the-Disconnected-Table-Trick/ba-p/279563.

In short, your 2 drop downs are disconnected tables. You use SELECTEDVALUE for example to grab the value in the dropdown slicer and you use that in your measure to display the appropriate KPI, value, etc. Works like a charm. So, think of it this way.

Line value measure = 
  SWITCH(SELECTEDVALUE('Line KPI'[KPI]),

    "Walk In",<do some calculation here>,

   "Something Else",<do some other calculation here>

  )