I have Miscanthus Variegatus in my front yard. I love the soft glow in the moonlight that makes it stand out from among darker green colors in the yard. With the clean vase-shape, it seems a shame to plant anything too tall in front of it. If you are looking for a grass to use, then I would suggest a few Elijah Blue fescues that have a nice low pincushion soft blue color. But overwhelmingly, I would choose a pennesetum 'hamelin' with it's low mounded shape and bunny tails. I have included a photo link for you.

Here is a link that might be useful: {{gwi:854014}}

deep roots ~ you hit the nail on the head!! I must agree that it would be a shame to plant anything in front of M. sin. Variegatus. It does have an amazingly elegant form from tip to toe. When I first read this post I was stumped and I guess that's why.
Actually tho, I had a friend who planted one of the low, fall blooming, creeping sedums in front of her Variegatus the results were spectacular! In the fall the burgandy flowers carpeting the ground against the white variegated grass .... wow!