What's the Right Shopping Cart Solution

I have 14,000 products, with roughly 10 different subscription pricing models, and I require the ability to take coupons.

I’ve setup a shopping cart with Marketpress and PayPal, and uploaded the 14,000 products using csv files. I’m using direct links to PayPal to sell the subscriptions, but this bypasses the ability to take coupons.

Membership isn’t really an option because the coupons aren’t working yet and there isn’t a good way to setup 14,000 products.

Any suggestions? How can I create a shopping cart with this many subscription products and take coupons?