Hi,
In HikaShop you can override all views, even backend ones.
So you can edit the view "order | export" and change the code which generate CSV/XLS files into something which will create a XML file compatible with your ERP system.
It is something which could be done using a little HikaShop plugin too, but the view override is easier.
Exporting a XML is not very complicated but the real problem is to determine the structure of the exported data. There is different ways to export the data in XML, using nodes or attributes. CSV have the advantage to be generic and compatible with a lot of softwares.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.