Using CD74HC4067 multiplexer with drumkit-kit (spikenzielabs) code

The default code for the "drumkit-kit" code only allows 6 analog drum pads. I was wondering if anyone knew how to use the CD74HC4067 analog/digital multiplexer with this code:

// User settable variables			
//*******************************************************************************************************************

unsigned char PadNote[6] = {52,45,41,58,40,51};         // MIDI notes from 0 to 127 (Mid C = 60)

int PadCutOff[6] = {600,600,600,600,550,600};           // Minimum Analog value to cause a drum hit

int MaxPlayTime[6] = {90,90,90,90,90,90};               // Cycles before a 2nd hit is allowed

#define  midichannel	0;                              // MIDI channel from 0 to 15 (+1 in "real world")

boolean VelocityFlag  = true;                           // Velocity ON (true) or OFF (false)





//*******************************************************************************************************************
// Internal Use Variables			
//*******************************************************************************************************************

boolean activePad[6] = {0,0,0,0,0,0};                   // Array of flags of pad currently playing
int PinPlayTime[6] = {0,0,0,0,0,0};                     // Counter since pad started to play

unsigned char status;

int pin = 0;     
int hitavg = 0;

//*******************************************************************************************************************
// Setup			
//*******************************************************************************************************************

void setup() 
{
  Serial.begin(57600);                                  // connect to the serial port 115200
}

//*******************************************************************************************************************
// Main Program			
//*******************************************************************************************************************

void loop() 
{
  for(int pin=0; pin < 6; pin++)
  {
    hitavg = analogRead(pin);                              // read the input pin

    if((hitavg > PadCutOff[pin]))
    {
      if((activePad[pin] == false))
      {
        if(VelocityFlag == true)
        {
//          hitavg = 127 / ((1023 - PadCutOff[pin]) / (hitavg - PadCutOff[pin]));    // With full range (Too sensitive ?)
          hitavg = (hitavg / 8) -1 ;                                                 // Upper range
        }
        else
        {
          hitavg = 127;
        }

        MIDI_TX(144,PadNote[pin],hitavg); 
        PinPlayTime[pin] = 0;
        activePad[pin] = true;
      }
      else
      {
        PinPlayTime[pin] = PinPlayTime[pin] + 1;
      }
    }
    else if((activePad[pin] == true))
    {
      PinPlayTime[pin] = PinPlayTime[pin] + 1;
      
      if(PinPlayTime[pin] > MaxPlayTime[pin])
      {
        activePad[pin] = false;
        MIDI_TX(128,PadNote[pin],127); 
      }
    }
  } 
}


//*******************************************************************************************************************
// Transmit MIDI Message			
//*******************************************************************************************************************
void MIDI_TX(unsigned char MESSAGE, unsigned char PITCH, unsigned char VELOCITY) 
{
  status = MESSAGE + midichannel;
  Serial.print(status);
  Serial.print(PITCH);
  Serial.print(VELOCITY);
}

I have very little coding experience so I have no idea what half of this code means. Any help is much appreciated.

See these pages:-
http://www.arduino.cc/playground/Learning/4051

http://www.thebox.myzen.co.uk/Hardware/MIDI_Footsteps.html

I have no idea what half of this code means

Time to start learning then. Extending what other people do is a good way to learn but you need to put in a bit of effort.
Basically you need to make the arrays bigger to take account of the greater number of inputs. Then you need to read those in by:-

  1. Setting the multiplexer select lines to the value of the input you want to read.
  2. Reading the value switched in.