Define some macros before including MIDI.h in your sketch to enable software serial.

src/MIDI.cpp

@@ -12,19 +12,18 @@
 #include <stdlib.h>
 #include "Arduino.h"            // If using an old (pre-1.0) version of Arduino,
                                 // use WConstants.h instead of Arduino.h
-#include "HardwareSerial.h"
-
-
-#if USE_SOFTWARE_SERIAL
+#if MIDI_USE_SOFTWARE_SERIAL
 
 // Note: Make sure the following relative path is correct.
 #include "../SoftwareSerial/SoftwareSerial.h"
-SoftwareSerial softSerialClass(SOFTSERIAL_RX_PIN,SOFTSERIAL_TX_PIN);
-
+SoftwareSerial softSerialClass(MIDI_SOFTSERIAL_RX_PIN,
+                               MIDI_SOFTSERIAL_TX_PIN);
 #undef  MIDI_SERIAL_PORT
 #define MIDI_SERIAL_PORT softSerialClass
 
-#endif // USE_SOFTWARE_SERIAL
+#else
+#include "HardwareSerial.h"
+#endif // MIDI_USE_SOFTWARE_SERIAL
 
 
 /*! \brief Main instance (the class comes pre-instantiated). */

src/MIDI.h

@@ -36,12 +36,6 @@
 
 #define MIDI_SERIAL_PORT        Serial      // Change the number (to Serial1 for example) if you want
                                             // to use a different serial port for MIDI I/O.
-
-#define USE_SOFTWARE_SERIAL     0           // Set to 1 to use SoftwareSerial instead of native serial ports.
-#define SOFTSERIAL_RX_PIN       1           // This pin number will be used for MIDI Input
-#define SOFTSERIAL_TX_PIN       2           // This pin number will be used for MIDI Output.
-
-
 #define USE_RUNNING_STATUS      1           // Running status enables short messages when sending multiple values
                                             // of the same type and channel.
                                             // Set to 0 if you have troubles controlling your hardware.
@@ -67,6 +61,18 @@
 #define MIDI_PITCHBEND_MAX      8191
 
 
+#ifndef MIDI_USE_SOFTWARE_SERIAL
+#define MIDI_USE_SOFTWARE_SERIAL 0
+#else
+  #if MIDI_USE_SOFTWARE_SERIAL
+    #if !defined(MIDI_SOFTSERIAL_RX_PIN) || !defined(MIDI_SOFTSERIAL_TX_PIN)
+    #error You need to define some pins to enable MIDI with software serial.
+    #endif
+  #endif
+#endif
+
+
+
 
 /*! Type definition for practical use 
     (because "unsigned char" is a bit long to write.. )