In my opinion better would be do not touch original ePO server because in present EEPC version is not possible to migrate machine keys. Thus better would be to register new AD server in ePO and synchronize user from it.
There is no problem to use ePolicy with one or more domains. ePo server could be a standalone server ou a domain server.
If you want to sync groups with AD,all you need to do is place the correct credentials in the 'Group details - Syncronization type' and in the 'Push Agent' option (if you want to automaticaly deploy the agent).
Althought, if you want to be able to login into ePO console with user-accounts from both domains, you must check this document:Supporting multiple domain controllers for user authentication in ePO 4.0 (KB53786) - https://kc.mcafee.com/corporate/index?page=content&id=KB53786&actp=search&viewlo cale=en_US&searchid=1291376373706I've done the above configuration in a customer with 3 domains.There one very important recomendation. The DNS must be working fine. So check the dns suffixs in the epo server or the stub zones in the dns server.Regards,Pedro