I have been selling single downloadable products through an "Sell Downloads" add-on. Now I want to add a shopping cart for downloadable items, ....I want to sell more than 1 downloadable item at a time. How do I do that? Which add-ons can I use for that please?
The 'Sell Downloads System' would require a fairly large amount of modifications to enable it to be used with a shopping cart, but it could be done.
The modifications are too numerous to be described completely, but basically you would have to change the database code and the 'buy-now' button from a single items code, to 'place in card' code. Then once you receive the ipn from paypal this would need to 'look-up' the items placed in the cart and generate download links for each item to be place in the e-mail notification for the product downloads.
As for add-ons you could look at the - Data Assist and Universal email from webassist at - http://www.webassist.com/dreamweaver-extensions/#alacarte.
Cartweaver is an e-commerce extension for DW in your choice of PHP, ASP or ColdFusion.
Also, supports digital download stores.
This from their blog