I think we should do a premier support ticket to get this done. I'm a little confused about what is going wrong and I think it would be best to work with you and your files directly to get this resolved.
I think you need to update the cart details calculation to include your new columns so they are passed to authorize.net. The success page is redirected after checkout and has to be specified in the authorize.net hidden form and configured from your authorize.net control panel.