I have tried  miner with my rig. I have Vegas 56 and have different versions, some are recognized as gfx900 and some as gfx901.
gfx900 are using generic OpenCL kernels, which are slower than optimized.
gfx901 are correctly recognized and using optimized OpenCL kernels

Here is the log :
GPU7 GPU7: Using generic OpenCL kernels (device name 'gfx900')
GPU8 GPU8: Using optimized OpenCL kernels (device name 'gfx901')