You should utilize the mediaelement.js shortcode [audio mp3=""] in your plugin. Maybe change the MP3 template, so that you can use HTML5 and Flash instead of your FLV player.

Also I’m looking for good ideas on how to build up a nice template with tables and all. I’ve just installed the “tablepress” plugin, to see if I can get some use of it.

I will also make some research on W3S, so that I can understand the HTML5 directive a little better.

Thank you for your input.