"Sadly, it's nVidia only."

Only if you want to use GPU rendering. It is faster with a nVidia card yes but it is not required. CPU can be done with any card.

Interesting.  How is the speed compared to LuxRender?

Hi WW  Comparison speeds between the CPU and GPU mode of iRAY in DAZ3D:

GPU(560TI 2GB ) with CPU(X5670 6core overclock'd 4.2GHz) mode scene bellow took 39mins 

CPU mode only(X5670 6 core overclock'd 4.2GHz) 1hour and 30mins

Lighting i've used only one spotlight and dome light(studio HDR from sIBL)

As you can see there is no difference between the CPU or GPU mode,only speed is there difference,as with every renderer,everything deepends on HW used.

Hope this helps 

Thanks,Jura