Why did you opt for the DL-DVI adapter rather than a mini-DisplayPort to DisplayPort cable? I have my rMBP plugged into a Dell U3011 most of the time and this seems like the most straightforward way.
I use an rMBP full time at work as well with no trouble using an Apple thunderbolt display, a 27 inch dell display (via mini displayport), and a fourth 1200p display via HDMI. I'd definitely suggest going for displayport if possible over the finicky DL-DVI adaptors.