Andy,
I figured out what part of the problem is. Us Pro Tools users on newer Macs cannot hear audio through our Pro Tools sound cards when using Quicktime and there is no option to use something other than Quicktime the way your site is programmed, using MP3s that are not downloadable in the particular player that your site is using. If we could download the files they will play fine, but as long as you program them the way they are, Pro Tools users will never hear them. You might want to consider an MP3 player like the site below uses, they play just fine and don't need to be downloadable.