Same experience only get 5 290 GPUs on a Asrock Bitcoin Board with 14.6.
Are you saying that new driver 14.6's card count limit is 5 cards?, that sucks!, damn!.
Well it fired up fine and was about 50% fastest but unstable since within the hour I lost the 6th card. Some weird error message in device manager, I rolled back the driver and still am getting better hash but not maxing it out man.