As promised over on my MP coupon hack page (https://premium.wpmudev.org/forums/topic/marketpress-per-item-coupons-beta), I'm sharing some work I've done on an audio store for Marketpress.
Basically what's included here are three components: a plugin (install in plugins directory), a Marketpress theme (install CSS file in Marketpress themes directory), and a couple of template files (install in your theme's directory).
I didn't take time to make the theme look great in very many themes, but you can customize it easily. I'm using Attitude by Theme Horse, and checked it in TwentyTwelve. If you have specific issues, I'm willing to help where I can.
The idea behind this project is to add music meta data, an audio player, etc., similar to http://wordpress.dwbooster.com/content-tools/music-store . 'Music Store' was lacking in the mature feature set I wanted, like an onsite shopping cart and coupons. So, I decided to add the functionality I needed from there to Marketpress!
A little background, I'm setting up a website for my music hobby (http://acoustics.pottervilla.com/ ) to sell CDs as well as album and single downloads. That's what this is really about. I'm not sure how it would work on a site that sells multiple types of items, as I've not tried that.
There's a readme.txt file that has installation instructions, usage, a little key to the MP functions I used, and some ideas on audio protection.
To add music metadata to your plugin, look for the new meta box on your content page called 'Song/Album Information'. Your product page and category page will be automatically themed as soon as you install the mp_product.php and mp_productlist.php files in your theme directory.
I designed the theme for use on my site with 'Attitude' by Theme Horse (available on WP.org). It also looks good with the default TwentyTwelve theme. If it breaks on your theme, you may have to edit mp_product.php, mp_productlist.php and probably acoustics.css.
Included with the plugin is a shortcode to display a product box. The syntax is like this: [productbox productid="75"] That lets you create a custom product page if you like, maybe a "bestsellers" page, or like me, a page for your album with productboxes for both the CD and MP3 editions.
This still may be sort-of buggy, but I trust you'll find it useful. And if you do find bugs, please let me know, and I'll do what I can to fix them. It works with Marketpress 2.8.7. Optional plugins are Facebook and MediaElement.js - HTML5 Audio and Video .
So here's the link: http://pubcdn.pottervilla.com/mp_audio_store_0.3.0.zip