I am glad you figured this out. The <!--more--> is a very old feature in WordPress, I'm not sure exactly if it works well with most themes and plugins these days.
The other fix would be to place your player above your blog posts or use the PowerPress quicktag and place the quicktag above the <!--more--> tag.
Example:
Blog post content ...
[powerpress]
<!--more-->
More blog post content...