Check out
http://www.clearkeysolutions.com/demos_subscription.php
It looks like the best subscription based drm i have seen so far. I've been trying for couple days to get drmnetworks working with my ccbill account and its still only 90% working. I'm sick and tired of dealing with them and not knowing what the problems are "exactly".
With clearkey it at least looks like the licenses will work for multiple processors by checking your htpasswd for an active un/pw. Unlike the processors having to pass data from one to the other.
good luck!