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You can try for example:

add_action( 'pre_get_posts', function( $q ) {
    if( $q->is_main_query() && $q->is_search() )
    {
        $q->set( 'nopaging', true );
        add_filter( 'posts_request', function( $request ) {
            $sql = 'YOUR EXTRA SQL QUERY';
            return "(" . $request . ") UNION ({$sql}) ORDER BY post_status DESC";
        });  
    }
});

where we use the no paging version to match your SQL query.

Update:

Well, if I understand your comment correctly you want to reuse the main search query in your extra SQL query. Here's one hacky version:

add_action( 'pre_get_posts', function( $q ) {
    if( $q->is_main_query() && $q->is_search() )
    {
        $q->set( 'nopaging', true );
        add_filter( 'posts_orderby', '__return_null' );
        add_filter( 'posts_request', function( $request ) {
            global $wpdb;
            $sql = strstr( $request, "AND {$wpdb->posts}.post_type IN", true );
            $sql = str_ireplace( "FROM {$wpdb->posts}", "FROM {$wpdb->prefix}software_and_hardware_post", $sql );
            $sql = str_ireplace( $wpdb->posts . '.*', 'ID, title as post_title, content as post_content ', $sql );
            $sql = str_ireplace( $wpdb->posts . '.post_title', 'title', $sql );
            $sql = str_ireplace( $wpdb->posts . '.post_content', 'content', $sql );
            $sql .= ' AND status = 1';
            $request = str_ireplace( $wpdb->posts . '.*', 'ID, post_title, post_content ', $request );
            return  "(" . $request . " ) UNION ({$sql}) ORDER BY post_status DESC";
        });
    }
});