Get attachment for custom post with parent and child taxonomies

I am trying to list the attachment of a custom post displayed by parent and child taxonomies.

The following code, which I appreciate someone else posting, works perfectly to display custom posts under a parent taxonomy (in this case a year) and then a child taxonomy.

<?php
// List posts by the terms for a custom taxonomy of any post type

$post_type = 'company';
$tax = 'client-topic';
$tax_args = array(
'order' => 'DESC',
'parent' => 0
);
// get all the first level terms only
$tax_terms = get_terms( $tax, $tax_args );
if ($tax_terms) {
foreach ($tax_terms as $tax_term) { // foreach first level term
// print the parent heading
?>
<h4 class="parent-term"><?php echo $tax_term->name; ?></h4>

<?php
// get all its children
$child_terms = ""; // first ensure this var is empty
$child_terms = get_terms ( $tax, array('order' => 'DESC', 'parent' => $tax_term->term_id) );
// store an array of child terms slug
$child_terms_array = array();
foreach ($child_terms as $child_term){
$child_terms_array[] = $child_term->slug;
}

// print the posts of the parent, but excluding the one which are also into a child term
$parent_args="";
$parent_args = array(
'post_type' => $post_type,
'tax_query' => array(
'relation' => 'AND',
array(
'taxonomy' => $tax,
'field' => 'slug',
'terms' => $tax_term->slug,
'include_children' => false,
'operator' => 'IN'
),
array(
'taxonomy' => $tax,
'field' => 'slug',
'terms' => $child_terms_array,
'include_children' => false,
'operator' => 'NOT IN'
)
),
'post_status' => 'publish',
'posts_per_page' => 6,
'order' => 'ASC',
);
// query the posts
$parent_query = null;
$parent_query = new WP_Query($parent_args);

if( $parent_query->have_posts() ) : ?>
<ul>
<?php while ( $parent_query->have_posts() ) : $parent_query->the_post(); ?>
<li><a href="<?php the_permalink() ?>">
<?php the_title(); ?>
</a>
</li>
<?php endwhile; // end of loop ?>
</ul>

<?php endif; // if have_posts()
wp_reset_query();

// if any, foreach child term, query the posts
if ( !empty($child_terms) ){
foreach ($child_terms as $child_term){
$child_args="";
$child_args = array(
'post_type' => $post_type,
'tax_query' => array(
array(
'taxonomy' => $tax,
'field' => 'slug',
'terms' => $child_term->slug,
'include_children' => false,
'operator' => 'IN'
)
),
'post_status' => 'publish',
'posts_per_page' => 6,
'order' => 'ASC',
);
// query the posts
$child_query = null;
$child_query = new WP_Query($child_args);

if( $child_query->have_posts() ) : ?>

<h4 class="child-term"><?php echo $child_term->name; ?></h4>
<ul>
<?php while ( $child_query->have_posts() ) : $child_query->the_post(); ?>
<li><a href="<?php the_permalink() ?>">
<?php the_title(); ?>
</a>
</li>
<?php endwhile; // end of loop ?>

</ul>

<?php endif; // if have_posts()

wp_reset_query();
} // end foreach #child_terms
}

} // end foreach #parent_term
}
?>

But the code displays post titles. I would like to instead get the attachment of each custom post and display the title and link. I have been able to do this in other scenarios by using this code directly below:

<?php 
$the_query->the_post();
			$args = array(		
			'order'          => 'DESC',
			'post_type'      => 'attachment',
			'post_parent'    => $post->ID,
			'post_status'    => null,
			'numberposts'    => 1,
		);
			$attachments = get_posts($args);
			if ($attachments) {
			foreach ($attachments as $attachment) { ?>

			<a href="<?php echo wp_get_attachment_url( $attachment->ID, true ); ?>"><?php the_title(); ?></a><br />
			<?php }
} 
?>

I am not skilled enough yet to combine the two pieces of code.

Does anyone have any ideas how to do this?

Thanks.