Get Unique Categories – Group By?

How about doing something like this?

//establish holders
$clients = array();
$media   = array();

//loop through gotten posts
foreach( $clients_query as $k => $v ) {
    //add to clients array
    if( !in_array( get_client( $v ), $clients ) )
        $clients[] = get_client( $v );
    //add to media array
    if( !in_array( get_medium( $v ), $media ) )
        $media[] = get_medium( $v );
}

You will need to replace get_client() and get_medium() with whatever you’re using to pull those values (presumably post meta, but you didn’t give enough info for me to feel confident in writing that code for you), then you will have an array of clients and an array of media. This same loop would allow you to remove duplicates with unset( $clients_query[$k] )…though if you do that you may want to reindex the array afterwards.