Some internal refactoring.

NTwain/Triplets/DGAudio/DGAudio.AudioFileXfer.cs

@@ -5,7 +5,7 @@ namespace NTwain.Triplets
 {
 	sealed class AudioFileXfer : OpBase
 	{
-		internal AudioFileXfer(TwainSession session) : base(session) { }
+        internal AudioFileXfer(ITwainSessionInternal session) : base(session) { }
 		/// <summary>
 		/// This operation is used to initiate the transfer of audio from the Source to the application via the
 		/// disk-file transfer mechanism. It causes the transfer to begin.

NTwain/Triplets/DGAudio/DGAudio.AudioInfo.cs

@@ -5,7 +5,7 @@ namespace NTwain.Triplets
 {
 	public sealed class AudioInfo : OpBase
 	{
-		internal AudioInfo(TwainSession session) : base(session) { }
+		internal AudioInfo(ITwainSessionInternal session) : base(session) { }
 		/// <summary>
 		/// Used to get the information of the current audio data ready to transfer.
 		/// </summary>

NTwain/Triplets/DGAudio/DGAudio.AudioNativeXfer.cs

@@ -5,7 +5,7 @@ namespace NTwain.Triplets
 {
 	sealed class AudioNativeXfer : OpBase
 	{
-		internal AudioNativeXfer(TwainSession session) : base(session) { }
+		internal AudioNativeXfer(ITwainSessionInternal session) : base(session) { }
 		/// <summary>
 		/// Causes the transfer of an audio data from the Source to the application, via the Native
 		/// transfer mechanism, to begin. The resulting data is stored in main memory in a single block.

NTwain/Triplets/DGAudio/DGAudio.cs

@@ -6,8 +6,8 @@ namespace NTwain.Triplets
 	/// </summary>
 	public sealed class DGAudio
 	{
-		TwainSession _session;
-		internal DGAudio(TwainSession session)
+        ITwainSessionInternal _session;
+        internal DGAudio(ITwainSessionInternal session)
 		{
 			if (session == null) { throw new ArgumentNullException("session"); }
 			_session = session;