IMac – How to connect an iMac 2011 to an HDMI laptop

The Apple mini-DisplayPort to VGA or HDMI adapter terminates the Thunderbolt chain where it is connected, so until Apple released new MacBook Pro with two Thunderbolt ports (similar to the iMac that has two ports) then you will only get one video signal from the device through the Thunderbolt port.

You may find an inexpensive USB to VGA solution to get around this limitation. Initially they were slower, but the newer ones are getting much faster and the software much better. You can then put the most important content on the Thunderbolt port and have the secondary display served over USB.

Should a Thunderbolt adapter come about that drives two displays, I'll update the answer, but nothing has been released (or even rumored) even though it's clearly something the protocol could support.

I like this knowledge base article for the clear deprecation of which Macs support two Thunderbolt displays and which ones only support one.

• Apple Thunderbolt Display (27-inch): Connection options for Thunderbolt Macs

I'm afraid that's not possible...

The closest you can get to that is by using Target Display Mode as described here. The problem, though, is that TDM is only available when running OS X on the iMac. Furthermore, you won't be able to use the iMac even though it's technically running.

Judging from this question here at Ask Different, TDM doesn't seem to support multiple displays while running anyway.

I've looked at this before and did some research for this question, and I was unable to find anything beyond streaming the contents in an AirPlay-like fashion, which I doubt is usable in your case.