I have a late 2009 27" iMac that I want to use as an external display for my new RetinaMBP. Currently I use the iMac and a 2nd 24"Dell monitor. My ideal setup would be the RetinaMBP driving both the iMac through the Belkin MiniDisplayPort to MiniDisplayPort connector and the Dell maybe via the HDMI to HDMI connection. Does anyone know if this is possible. I've found confirmation that the imac can be used in Target display mode even from a new Thunderbolt laptop using the the MDP-MDP cable and not using a TB cable but I wondered if I can also drive the Dell monitor via the HDMI port?? Thanks to anyone who knows or has tried this.