Changing DrumKit Sketch to Only Read One Hit at a Time

I could believe you are not trying. I said:-

It goes just before the closing brace of the while statement.

If you click on the opening brace the closing brace gets highlighted. Remember that, in the mean time:-

void loop() 
{
  int pin = 0;
  boolean noHit = true;
  while(pin < 6 && noHit){
    hitavg = analogRead(pin);                              // read the input pin
    if((hitavg > PadCutOff[pin]))
    {
       MIDI_TX(144,PadNote[pin],hitavg); 
        noHit = false;
      }
      pin++;
    }    
    delay(100); // adjust for length of time to play note
        MIDI_TX(128,PadNote[pin],127);
        noHit = true; 
      }