Ah-ha! Makes sense to me now. Basically a play on an english brown of some sort with a german twist.
Aside from various crystal malts, I've used amber, brown, pale chocolate, midnight wheat, mild malt. Granted, all of those were not german brand malts. Keeping with the german ingredient and "twist" nature of this beer, maybe some chocolate wheat or chocolate rye. You could also toast some of your base munich to get that toasty/nutty quality from it for an amber/brown-like character.