In the Business edition of HikaShop, you can select access levels for prices, products, categories, discounts, etc so that will enable you to do that. You can see that on our demo website: demo.hikashop.com/administrator
It's really easy to do. When you edit a product, you will have an access level zone where you can just select which groups can see the product. For the prices you will get a small button or each one of them which will open a popup in order to select the access levels, etc...
If you want to sell mp3s, you can add your mp3 in the "files" zone when creating/editing a product. Then, when someone buy that product, the files will be downloadable on the order page (a link is sent to the order page in the emails sent to the user).