Just FYI, this question probably borders on **too localized**, as it is specific to the Oenology Theme.

That said, here's where I *think* you're having a problem: Oenology enqueues two style sheets:

1. `style.css`, directly in the document head (thus *before* `wp_head()` is fired)
2. `{varietal}.css`, at `wp_enqueue_scripts`, with priority `11`, in `functions/dynamic-css.php`:

 /**
 * Enqueue Varietal Stylesheet
 */
 function oenology_enqueue_varietal_style() {

	 // define varietal stylesheet
	 global $oenology_options;
	 $oenology_options = oenology_get_options();
	 $varietal_handle = 'oenology_' . $oenology_options['varietal'] . '_stylesheet';
	 $varietal_stylesheet = get_template_directory_uri() . '/varietals/' . $oenology_options['varietal'] . '.css';
	
	 wp_enqueue_style( $varietal_handle, $varietal_stylesheet );
 }
 // Enqueue Varietal Stylesheet at wp_print_styles
 add_action('wp_enqueue_scripts', 'oenology_enqueue_varietal_style', 11 );

The varietal stylesheet, which applies the "skin", enqueues at priority `11`, to ensure that the base stylesheet, `style.css`, loads *first*, and the varietal stylesheet loads *second*, in order to cause the correct cascade.

So, if you need to override the *varietal* stylesheet, simply enqueue your second stylesheet *after* the varietal stylesheet; i.e. with a priority of at least `12` or greater.