S2Members WP e-Commerce?

Hi all,
I need to create a site which will be selling products, some of which will be sold (with commision) on behalf of the site members. So I’ve been looking at WP e-Commerce (https://getshopped.org) with the gold cart, Multiple Vendors & also the Members Only modules.
However the Members only module gives very little information, or is lacking in facilities to the likes of S2 Members, I kind of need to functionality of S2 Members, with the sales ability of WP e-Commerce.
And what’s more they need to be able to process all payments through 2CheckOut – just to make it that bit harder.

Anyone any suggestions for optional plugins, or how this could be done?