mp3 player (universal) problem on this theme only

I am using the current version of WP and a heavily modified version of Twenty Eleven. I need an audio player, one that can be played from the page it’s on without asking the viewer to download, but every single one that I have tried either doesn’t show up at all or just has the link to let someone download. I have tried on the exact same theme, the original unaltered twenty eleven (on another WP account) and it worked fine. Please help me, it’s really important that I get this to work and I have tried everything I could think of, and looked through the forums multiple times and found nothing either.

Here are the mp3 players that I have already used that didn’t work for me:
mp3-jplayer
mp3 player
wpaudio
wp audio player
simplistic haiku minimalistic audio player

All of the above (except the haiku one which I didn’t try on another but I’m sure it’s the same) worked on my other wordpress site just fine.

Everything else I tried:
*switching themes: yes, everything works if I switch themes, even in the same account, but I need THIS one so that’s not an option.
*updated adobe flash player
*deleted all the other plugins, still no luck
*tried several different browsers
*tried the original twenty eleven theme that mine is based on, worked fine.

Something in my specific modified theme is the problem, I’m thinking I probably messed something up in the process of customization, but I don’t know where to look. I normally only touch the design-related files, nothing deeper than that. I would really appreciate any suggestions of things that could help or things that I haven’t tried that I could look at. Thanks

PS. the link to the site that’s connected with this profile isn’t the one in question, it’s just a sandbox