WordPress eCommerce Advice

We have a company website built using wordpress. We also have a separate website that is hosted that we use for our clients to log onto and purchase approved products from. They login and can see a list of products with the price they pay for it.

I require an ecommerce plugin that is capable of the following, even if it means purchasing add ons:

Need to be able to restrict who can access the shop. I use s2 member so could do it based on role possibly.

Need to be able to apply group pricing to products, each customer group pays a different price for each product.

Need to be able to accept purchase order numbers as payment.

Need users to be able to view orders placed and edit addresses from the profile.

Would also ideally like the user account to integrate with WordPress so they dont require a seperate login to the site login.

Any help or guidance would be appreciated.