You can upgrade to Sound Taxi because it appears that has the same functionality as DRM Converter Professional. However, keep in mind that these applications are somehow different one from each other due to the functionality they offer, but the basic principle remains.
Give SoundTaxi a try to test it if it works for you or not.
- Note: I've searched the web to find DRM Converter Professional, but it appears that it has been discontinued since I didn't find anything about it.
