DRM has proven to be a business killer. There are many people who will simply not purchase anything from a company that uses DRM. You may note that Apple has dropped it for iTunes purchases. You may also note that the New York Times discontinued the TimesSelect subscription service because the revenue from subscriptions was far lower than they expected, and the columnists whose work was so protected lost most of their audience. Companies that offer free samples and DRM-free content have far more sales than companies that use DRM, an excellent example is Baen Books' Free Library and Webscriptions. My suggestion is to drop DRM completely.
FTC Town Hall to Address Digital Rights Management Technologies - Event Takes Place Wednesday, March 25, 2009, in Seattle #539814-00099
FTC Town Hall to Address Digital Rights Management Technologies - Event Takes Place Wednesday, March 25, 2009, in Seattle