Hi John,
You may have seen this list of PMs that can link to AC.
http://amazingcharts.com/services/interfaces/practice-management/I would look at the ones that don't have an asterisk after them as they will have a direct link and don't need an interface.
There is a benefit to the chaos level in an office in having the medical staff learn the ehr at a different time than when the billing staff learn the PM.
I hope that you are not in a situation where you will have to stop using the PM you have without future access. The best scenario is where you can keep using your PM for your old charges so you don't have to do a migration and your staff can stay efficient with software they know until it's not needed. Transition means decreased production.
As you may know, AC is pursuing a relationship with a secret PM vendor that would probably have an optimal link and essentially be integrated. If you could wait a while and use AC with your old PM, you might be happier with the choice AC makes for the PM. Why it is taking so long to establish this relationship, I can only wonder. But for me, my wife is happy using our old PM until AC unveils the new PM vendor. Happy wife, happy life.