Does the Apple Mini DisplayPort to Dual-Link DVI adapter passthrough HDCP?
Here's what Apple says about this: 


  Apple Mini DisplayPort adapters that offer digital connections—such as
  the Apple Mini DisplayPort to Dual-Link DVI adapter and the Apple Mini
  DisplayPort to DVI adapter—support HDCP content. Apple Mini
  DisplayPort adapters that offer analog connections—such as the Apple
  Mini DisplayPort to VGA adapter—do not support HDCP content.


Also, I found this answer on an Apple site but I can't verify if it's correct so YMMV:


  Here is what I found a) Mini DP to DP will offer full resolution 2560
  X 1080 @ 60 Hz but HDCP content from iTunes is not permitted, ie. will
  not run; b) HDMI adapter to DVI-D allows HDCP content to run but the
  resolution is limited to 1920 x 1080 @ 60Hz; c) HDMI to HDMI also does
  not offer full resolution but allows access to HDCP content; finally,
  the only configuration that offers both full resolution and HDCP is
  with Mini Display Port to Dual DVI-D cables.