At the moment you can only use one Kona in a Mac using the retail drivers. AJA has been saying for 12-18 months there would be multi card support. The only way to get more than one card to work, is to get there SDK and go to writing new drivers.
Decklink does support two cards at once using there retail drivers. There are applications out there that you can use, like Softron Media MovieRecorder to ingest two streams at the same time on one workstation. I’ve got 11 ingest stations with dual inputs capabilities. I’m more of an AJA fan, but due to there single card only support at the moment, I had to purchase Decklink. The dual input does save on hardware and software licensing.
With both manufactures there will be a two card limit with the retail drivers, this is in part to a Quicktime limitation.
-andre