May I ask for help with the following?

I am attempting to connect and control three pieces of household electronic equipment by computer through a GlobalCache GC-100 and iTach. As you will see in the following code, I created a class-instance of GlobalCacheAdapter that communicates with each piece of equipment. Although the code seems to work well in controlling the equipment, I am having trouble updating controls with the feedback from the equipment. The procedure "ReaderThreadProc" captures the feedback; however I don't know how to update the associated TextBox with the feedback. I believe that I need to create an EventHandler to notify the TextBox of the available update; however I am uncertain as to how an EventHandler like this would be implemented.

Any help wold be greatly appreciated.

  using System;
  using System.IO;
  using System.Net;
  using System.Net.Sockets;
  using System.Threading;
  using System.Windows.Forms;

  namespace WindowsFormsApplication1
  {
       public partial class Form1 : Form
       {

             // Create three new instances of GlobalCacheAdaptor and connect.
             // GC-100 (Elan) 192.168.1.70 4998  
             // GC-100 (TuneSuite) 192.168.1.70 5000  
             // GC iTach (Lighting) 192.168.1.71 4999

             private GlobalCacheAdaptor elanGlobalCacheAdaptor;
             private GlobalCacheAdaptor tuneSuiteGlobalCacheAdaptor;
             private GlobalCacheAdaptor lutronGlobalCacheAdaptor;

             public Form1()
             {
                  InitializeComponent();

                  elanGlobalCacheAdaptor = new GlobalCacheAdaptor();
                  elanGlobalCacheAdaptor.ConnectToDevice(IPAddress.Parse("192.168.1.70"), 4998);
                  tuneSuiteGlobalCacheAdaptor = new GlobalCacheAdaptor();
                  tuneSuiteGlobalCacheAdaptor.ConnectToDevice(IPAddress.Parse("192.168.1.70"), 5000);
                  lutronGlobalCacheAdaptor = new GlobalCacheAdaptor();
                  lutronGlobalCacheAdaptor.ConnectToDevice(IPAddress.Parse("192.168.1.71"), 4999);

                  elanTextBox.Text = elanGlobalCacheAdaptor._line;
                  tuneSuiteTextBox.Text = tuneSuiteGlobalCacheAdaptor._line;
                  lutronTextBox.Text = lutronGlobalCacheAdaptor._line;
           }

           private void btnZoneOnOff_Click(object sender, EventArgs e)    {    elanGlobalCacheAdaptor.SendMessage("sendir,4:3,1,40000,4,1,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,181,21,800" + Environment.NewLine); }
           private void btnSourceInput1_Click(object sender, EventArgs e) {    elanGlobalCacheAdaptor.SendMessage("sendir,4:3,1,40000,1,1,20,179,20,179,20,179,20,179,20,179,20,179,20,179,20,278,20,179,20,179,20,179,20,780" + Environment.NewLine); }        
           private void btnSystemOff_Click(object sender, EventArgs e)    {    elanGlobalCacheAdaptor.SendMessage("sendir,4:3,1,40000,1,1,20,184,20,184,20,184,20,184,20,184,20,286,20,286,20,286,20,184,20,184,20,184,20,820" + Environment.NewLine); }

           private void btnLightOff_Click(object sender, EventArgs e)     {    lutronGlobalCacheAdaptor.SendMessage("sdl,14,0,0,S2\x0d"); }
           private void btnLightOn_Click(object sender, EventArgs e)      {    lutronGlobalCacheAdaptor.SendMessage("sdl,14,100,0,S2\x0d"); }

           private void btnChannel31_Click(object sender, EventArgs e)    {    tuneSuiteGlobalCacheAdaptor.SendMessage("\xB8\x4D\xB5\x33\x31\x00\x30\x21\xB8\x0D"); }
           private void btnChannel30_Click(object sender, EventArgs e)    {    tuneSuiteGlobalCacheAdaptor.SendMessage("\xB8\x4D\xB5\x33\x30\x00\x30\x21\xB8\x0D"); }
      }
}

public class GlobalCacheAdaptor
{
      public Socket _multicastListener;
      public string _preferredDeviceID;
      public IPAddress _deviceAddress;
      public Socket _deviceSocket;
      public StreamWriter _deviceWriter;
      public bool _isConnected;
      public int _port;
      public IPAddress _address;
      public string _line;

      public GlobalCacheAdaptor() { }
      public static readonly GlobalCacheAdaptor Instance = new GlobalCacheAdaptor();

      public bool IsListening { get { return _multicastListener != null; } }

      public GlobalCacheAdaptor ConnectToDevice(IPAddress address, int port)
      {
            if (_deviceSocket != null) _deviceSocket.Close();
            try
            {
                  _port = port;
                  _address = address;
                  _deviceSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
                  _deviceSocket.Connect(new IPEndPoint(address, port)); ;
                  _deviceAddress = address;
                  var stream = new NetworkStream(_deviceSocket);
                  var reader = new StreamReader(stream);
                  var writer = new StreamWriter(stream) { NewLine = "\r", AutoFlush = true };
                  _deviceWriter = writer;
                  writer.WriteLine("getdevices");
                  var readerThread = new Thread(ReaderThreadProc) { IsBackground = true };
                  readerThread.Start(reader);
                  _isConnected = true;
                  return Instance;
           }
     catch { DisconnectFromDevice(); MessageBox.Show("ConnectToDevice Error."); throw; }
}
     public void SendMessage(string message)
     {
           try
           {
                 var stream = new NetworkStream(_deviceSocket);
                 var reader = new StreamReader(stream);
                 var writer = new StreamWriter(stream) { NewLine = "\r", AutoFlush = true };
                 _deviceWriter = writer;
                 writer.WriteLine(message);
                 var readerThread = new Thread(ReaderThreadProc) { IsBackground = true };
                 readerThread.Start(reader);
           }
           catch { MessageBox.Show("SendMessage() Error."); }
    }

    public void DisconnectFromDevice()
    {
         if (_deviceSocket != null)
         {
               try { _deviceSocket.Close(); _isConnected = false; }
               catch { MessageBox.Show("DisconnectFromDevice Error."); }
               _deviceSocket = null;
         }
        _deviceWriter = null;
        _deviceAddress = null;
    }

    private void ReaderThreadProc(object state)
    {
          var reader = (StreamReader)state;
          try
          {
              while (true)
              {
                 var line = reader.ReadLine();
                 if (line == null) break;
                 _line = _line + line + Environment.NewLine;
              }
             // Need to create EventHandler to notify the TextBoxes to update with _line
           }
           catch { MessageBox.Show("ReaderThreadProc Error."); }
    }

}