How do I handle an int** in Ada?

I'm trying to call SDL_LoadWAV using a pre-made binding to the C library from which it comes. SDL_LoadWAV is just a wrapper for SDL_LoadWAV_RW:

function SDL_LoadWAV
 (file      : C.char_array;
  spec      : access SDL_AudioSpec;
  audio_buf : System.Address;
  audio_len : access Uint32) return access SDL_AudioSpec
is
begin
  return SDL_LoadWAV_RW
      (SDL_RWFromFile (file, C.To_C ("rb")),
       1,
       spec,
       audio_buf,
       audio_len);
end SDL_LoadWAV;

Here is the prototype of the function in C:

SDL_AudioSpec* SDL_LoadWAV_RW(SDL_RWops*     src,
                          int            freesrc,
                          SDL_AudioSpec* spec,
                          Uint8**        audio_buf,
                          Uint32*        audio_len)

(See here for more information)

Now as you can see, it passes a Uint8 (unsigned 8-bit integer) array by reference, in the form of a Uint8**. This is causing me a great bit of vexation. Here is the appropriate binding:

function SDL_LoadWAV_RW
 (src       : access SDL_RWops;
  freesrc   : C.int;
  spec      : access SDL_AudioSpec;
  audio_buf : System.Address;
  audio_len : access Uint32) return access SDL_AudioSpec;
pragma Import (C, SDL_LoadWAV_RW, "SDL_LoadWAV_RW");

As you can see, the binding maps the Uint8** to a System.Address. I've tried a couple of tricks to get that data where I want it to go, but nothing seems to work. Right now, my code looks like this (it has a few custom types and exceptions in it):

type Music is new Resource with
record
    --Id : Integer; (Inherited from Resource)
    --Filename : Unbounded_String; (Inherited from Resource)
    --Archive_Name : Unbounded_String; (Inherited from Resource)
    --Zzl_Size : Integer; (Inherited from Resource)
    Audio : access SDL_AudioSpec_Access;
    Length : aliased Uint32;
    Buffer : System.Address;
    Position : Integer := 1;
end record;

overriding procedure Load(Mus : in out Music) is
    Double_Pointer : System.Address;
begin
    Log("Loading music " & To_Ada(Get_Audio_Filepath(Mus)));
    Audio_Load_Lock.Seize;
    if null = SDL_LoadWAV(Get_Audio_Filepath(Mus), Mus.Audio.all, Double_Pointer, Mus.Length'access) then
        raise Audio_Load_Failed with To_String(Mus.Filename) & "&Stack=" & Get_Call_Stack;
    end if;
    Log("Music length =" & Integer'Image(Integer(Mus.Length)));
    declare
        type Sample_Array is array(1..Mus.Length) of Uint8;
        Single_Pointer : System.Address;
        for Single_Pointer'address use Double_Pointer;
        pragma Import(Ada, Single_Pointer);
        Source : Sample_Array;
        for Source'address use Single_Pointer;
        pragma Import(Ada, Source); 
        Dest : Sample_Array;
        for Dest'address use Mus.Buffer;
        pragma Import(Ada, Dest);
    begin
        Dest := Source;
    end;
    Audio_Load_Lock.Release;
end Load;

But, like more or less everything else I've tried, I get a PROGRAM_ERROR/EXCEPTION_ACCESS_VIOLATION when the Load function is executed.

Can anyone figure out how I need to handle this System.Address? Thanks!