>AObject.SaveToStream( Stream );
を

if AObject is THoge then
begin
　Stream.Write(THoge(AObject).Buffer^, THoge(AObject).BufferSize);
　Stream.Write(THoge(AObject).Name[0], Length(THoge(AObject).Name));
　...
end
else if AObject is TFoo then
begin
　...
end
else
...
と直せばできるＹＯ！