I can get to wp-content/plugins/amazon-s3-cloud-html5-mp3-player/html5/facebook.png and
wp-content/plugins/amazon-s3-cloud-html5-mp3-player/html5/amazon-s3-cloud-mp3-player.png
Without issue
When I installed the plugin the html5full.php is at
wp-content/plugins/amazon-s3-cloud-html5-mp3-player/html5/html5full.php
I’ve also updated the entire plugin folder to be 755 permissions – the server is running PHP 7.1 – as I mentioned I got the same results on 2 different servers and a local install
As a test I copied the entire plugin folder to /player and it worked here
I then updated the iframe to point to here and it’s working – not ideal but I’ll use this way if I have to