E28s use a hydraulic 'bomb' setup. A little bit of a different setup compared to a regular booster. Check out realoem.com, it should give you an idea of what lines and stuff you will need to run if you choose to go with the E28 setup.
A dual master system is rather pricey IMO, and then the hassle of setting things up with pedal ratios, balance bars, etc etc... I sure as hell would be too lazy for all that lol. Hold out for a booster. Try to find a used one as its much cheaper... I do have a line on a new one if you are interested, but its pretty pricey.