Over the weekend, just as I was on the fence about ordering a USB->DVI adapter I saw a sale on a newer-than-mine Thunderbolt hub whose only improvement was an HDMI port. (At the cost of a Firewire port, natch.)
When the hub came today and I swapped it for the one that connects my laptop to a Displayport display (and a USB hub), I found that when I plugged in a third monitor by HDMI, the second (Displayport) would immediately turn off.
Some — too late — searching revealed a flaw in my plan: with both the Elgato and Belkin hubs, connecting an HDMI display will disable another monitor that is connected by miniDisplayport.
cf. Elgato help and Belkin help.
Mentioning this here as a buyer beware. The limitation was discussed in the help docs, but not on the sales sites or on the .
Ok, what this means is: you can have a Thunderbolt port that connects to a Thunderbolt display and also connects to a third screen by HDMI, but you can't use a Thunderbolt hub to connect a Macbook Air to two external monitors that are not Thunderbolt displays.
With all the parts I already have, I was hoping to drive two additional screens from a 2014 MacBook Air — ideally two of these — but it looks like one of those screens will have to be an Apple Thunderbolt display which is both too glossy and too expensive, even on Craigslist. For the money, it probably makes more sense to get an 2010–2012 Thunderbolt iMac and go back to using Synergy or Teleport instead of connecting the laptop to either of the larger screens.
Which is basically what I already had before I loaned away my iMac to a friend who needed a computer. OK. That settles it. Sticking with what I have until another iMac turns up for more or another computer for him.