I had no idea that you could brickwall running line in... learn something new everyday!
I still think you might be right Tim. I'm not sure you will brickwall the D100 on line in, but maybe.
More than likely the issue Kyle is having is with the MV100. I had one for awhile and ran it with km184s that are pretty hot and had no -10db pad. And I got a number of boughts of brickwalling before I figured out the problem. The MV100 can take in a very hot signal on its input, but not on its output after the minimum +20db gain boost. If you dig around the Oade archives, you can find my much more detailed post on this subject, along with all the specifications for the MV100.
I finally went in and modified the gain structure of the MV100 so that it provided less gain, and all the problems went away.
Oh, by the way, at the time I was having the brickwalling problems, I was not running the MV100 into a D100, but into either an Apogee AD500e or line-in to an Aiwa HDX3000 dat (same as the Marantz pmd700).