Since these cars don't run a mass air flow sensor, instead use map sensors to simulate a virtual mass air flow, these cars do not suffer from lean faults due to air leaks as often, unless its a specific one cylinder air leak in the runner.
If plugs are good I would lean towards the injector, especially being as you also have mixture faults. One problem causing both issues is much more likely than two completely unrelated issues at the exact same time. A failed DME usually just quits, I have not fixed any misfire issues on any bmw with replacement of a DME. Start with the basics.
Goes back to an old saying of if you hear hoof steps think horses not zebras.
BMW master tech
2010 E92 335i 6-speed 25k miles. - For sale.
1989 E30 325i coupe 5-speed DD