[Khronos]

Gracias por responder cHackAll, ya encontré la forma de solucionar el problema:

Código Delphi [-]
unit Global;

interface

uses Messages, Classes;

//color = $00FFDDBB;

type
  TPhxMessage = packed record
      DestHandle: THandle;
      Str: string[255];
  end;

const
  Mapping = 'OPAMS-14ASD-MU1EX';
  Mutex = 'E51BA-9QIOSAD-PHOENIX';
  WM_TRANSFER = WM_USER + 1;

var
  Index: integer = 0;
  UpdateOpen: boolean = false;
  UpdateSlider: boolean = false;
  WiniPath: string;

  PhxMessage : ^TPhxMessage;
  mhandle, nHandle: THandle;
  CustomList: TStringList;
  Sychronized: boolean = true;

implementation

end.

Código Delphi [-]
program phxmp;

uses
  ComCtrls,
  Forms, Classes,
  XPMan, Messages,
  SysUtils,  Windows, dialogs,
  frm_main in 'frm_main.pas' {FMain},
  frm_skins in 'frm_skins.pas' {FSkins},
  PlayerUtils in 'PlayerUtils.pas',
  Global in 'Global.pas',
  uThreadFiles in 'uThreadFiles.pas',
  uPlayList in 'uPlayList.pas';

{$R *.res}

begin
  WiniPath:= ExtractFilePath(paramstr(0)) + 'Options.ini';
  Application.Initialize;
  Application.CreateForm(TFMain, FMain);
  Application.CreateForm(TFSkins, FSkins);


  CreateMutex(nil, True, Mutex);
  if GetLastError = ERROR_ALREADY_EXISTS then
  begin
     if ParamCount = 1 then
      begin
        nHandle:=OpenFileMapping(FILE_MAP_ALL_ACCESS,False, pchar(Mapping));
        if nHandle = 0 then raise Exception.Create('Error ¿?');
        PhxMessage:= MapViewOfFile(nHandle,FILE_MAP_ALL_ACCESS,0,0,0);
        PhxMessage^.Str:= paramstr(1);
        PostMessage(PhxMessage^.DestHandle, WM_TRANSFER, 0 ,0);
        UnmapViewOfFile(PhxMessage);
        CloseHandle(nHandle);
      end;
      ExitProcess(0);
  end else
    begin
     mHandle:= CreateFileMapping($FFFFFFFF,nil,PAGE_READWRITE,0, SizeOf(TPhxMessage), pchar(Mapping));
     PhxMessage:=MapViewOfFile(mHandle, FILE_MAP_WRITE,0,0,0);
     PhxMessage^.DestHandle:= FMain.Handle;
    end;

  Application.Title:= 'Phoenix Media Player';
  Application.Run;
end.

Y después en el Form:

Código Delphi [-]
  public
    procedure HookMessage (var Msg: TMessage); message WM_TRANSFER;
  end;

var
  FMain: TFMain;

implementation

{$R *.dfm}

procedure TFMain.HookMessage(var Msg: TMessage);
var
Thread: TMFThread;
begin
    if CheckCompability(PhxMessage^.Str) = true then
      begin
        CustomList.Add(PhxMessage^.Str);
        Thread:=TMFThread.Create(CustomList);
        CustomList.Clear;
      end;
end;

Funciona perfectamente, registro las extensiones en el registro y solo se abre un única instancia de mi aplicación. Pero me surge un error, cuando abro muchos archivos por la sincronización de los thread que espero resolver pronto.

Muchas gracias Saludos.

PD: Tengo que resolver el problema del BufferOverflow...