**Update-- I just noticed that the quantity in the paypal shopping cart shows '1' no matter how many items are in the cart. Not sure if its related but thought it was worth posting.
This is correct behavior; the items in the cart are grouped into one item (music store purchases) and then processed that way; when you return to the site the paypal transaction is matched back to a cart which has the multiple items in it.
as far as the transaction amount not matching, does the paypal checkout page show the correct amount that is in the cart?
Can you check for error logs and post them here; (error logs could be in your components/maian_media folder.
Also post what version of PHP your server is using for your site;