Using both HDMI and display port?

Hmm. Well, having a "fake" monitor plugged into a Mini Displayport port and a real TV plugged into the HDMI port should be no different than having two real monitors plugged into the Mac, and that certainly works fine. (I'm looking at two monitors plugged into my Mini at this moment.)

What I'm more surprised about is why you would even need the adapter in the first place. If you've got a monitor (or TV) plugged into the HDMI port, even if it is off, I think the Mini should be able to recognize that a monitor is plugged in. In which case, you really shouldn't need the "headless" adapter at all.

I suppose a quick test would be, examine the screen sharing performance when the HDMI is plugged in to the Mini (and the TV is off), as compared to when the HDMI cord is disconnected from the Mini. I'll bet you that having a switched-off TV plugged into the Mini is just as good as having a dummy adapter plugged in would be. (If both options are obviously slower than when the TV is being used as the computer's monitor, then my apologies for being completely off-base here. )

 

I'm running two 23 inch screens using the HDMI & TB and with Airplay through TV to a 42 inch TV as a 3rd screen.