Using both thunderbolt ports for video on new iMac

I recently purchased the new 27in iMac and was planning on using both of the thunderbolt ports for external monitors. I purchased a thunderbolt to DVI cable to connect a samsung monitor, and I purchased a thunderbolt to HDMI cable to connect my visio HDTV as a third. The HDMI connected to visio works great by itself, and the DVI connected to Samsung monitor also works great, but when they are both plugged in, I lose the picture on one of them. Also, when they are both plugged in, in my display preferences I see three monitors and am able to arrange them however I like (I prefer the VISO above iMac monitor and Samsung to the left), but I still can't get a working picture from both at the same time. Also the Samsung flickers when both are plugged in. Is there not enough power/data to run both monitors simultaneously?