I'm also not familiar with the "Curve_ink=" command in the ink descriptor file. Could you explain that a bit more?
To me what seems the most straight forward is to create a .quad file using a decent ink descriptor file as a starting point, then directly editing the ink curve numbers in the .quad file (via excel to preview the resulting ink curve and density response) to shape each curve individually to the desired blend and ultimately shape the look of the final grayscale. I need to do a bit more research in terms of how specific inks combine to achieve a desired density, but once I get a feel for that, this seems like the most straight forward (although clumsy and cumbersome) way to get the most fine-tuned control of every aspect of the curve.