The Payment Processor we are making this mod for is Accelerated Payment Technologies.
http://acceleratedpay.com/ Their middleware product is called X-Charge. It is on the PCI Complaince Validated list right before X-Payments. Our solution will be to use X-Charge in an iframe that is loaded into a modal after checkout, which takes X-Cart out of scope. Authorize.net's DPM is still questionable to me, since the form is being served by X-Cart. The post is being handled by Auth.net, which is good, but I have read it is questionable making DPM not pass for some, while it will for others. We considered this, but it was not an option when we found that out.. I wouldn't want it to be ok for some and not others.. The variable would be the payment processor's choice of PCI scanning company.. too many variables.
We are almost finished with the certification then our customers will be changing to the new processor. I really would like to make this module available as an option for X-Cart users for free, and again the only stipulation is that they will need to go through us to change Payment processors. I should have more information within the next few weeks. I hope this helps. I would also welcome anyone's suggestions on how to make this available to X-Cart users other than this thread.. Thanks!!
By the way, the other question... Hard Hat Hosting ROCKS!!!