Here is 2CheckOut (2CO) reply regarding integrating 2CO to DNN system:

"A third party shopping cart is not necessary in order to use our
service. We provide you with the option of using our easy-to-use Plug-N-Play
shopping cart. Our PNP shopping cart uses simple HTML links, so you do not
need to install extra software.

However, if you wish to use a third party shopping cart with our service, you
may do so. The 2Checkout service generally is compatible with the following
third party shopping carts:

    * Any shopping cart compatible with the Authorize.net parameter set,
provided that it allows you to change the gateway URL. Nearly all shopping
carts today support the Authorize.net standard.
    * Any shopping cart that advertises 2Checkout support on their Web site
should work with our service.
    * Miscellaneous shopping carts. If your shopping cart does not fit either
of the above criteria, or if it is simply in question, there is a way to
determine whether or not your cart supports our service. Simply check with the
manufacturer of the shopping cart to confirm it's compatibility. You can
contact the maker personally, go to their Web site, or read any documentation
that may have been provided with the cart, itself."

So, any help with changing Authorize.net gateway URL with 2CO one or another ideas regarding other solution to be compaiable with DNN?