I am not sure if I am going to propose a different approach or if I am about to tell with different words what you already meant with your original question, but as you want the nodes to be the files, I would rather generate the nodes starting from the files, rather than associating existing nodes with existing files.
In generic terms I would do it programmatically: for each existing files in your import directory I would build the $node
object and then invoke node_save($node)
to store it in Drupal.
Of course in building the $node
object you will need to invoke the API function of the module you are using to manage the files. Here's some sample code I wrote to do a similar task. In this scenario I was attaching a product sheet to a product (a node with additional fields), so...
field_sheet
was the CCK field for the product sheet in the product node
product
was the node type
$sheet_file
was the complete reference (path + filename) to the product sheet file.
So the example:
// Load the CCK field
$field = content_fields('field_sheet', 'product');
// Load the appropriate validators
$validators = array_merge(filefield_widget_upload_validators($field));
// Where do we store the files?
$files_path = filefield_widget_file_path($field);
// Create the file object
$file = field_file_save_file($sheet_file, $validators, $files_path);
// Apply the file to the field, this sets the first file only, could be looped
// if there were more files
$node->field_scheda = array(0 => $file);
// The file has been copied in the appropriate directory, so it can be
// removed from the import directory
unlink($sheet_file);
BTW: if you use a library to read MP3 metadata, you could set $node->title and other attributes in a sensible way.
Hope this helps!