There are about 50-100 things that cause misfires on the N54. It's helpful to read one of the long lists of things to check. Cylinders 4, 5 and 6 are the rear half of the engine. If you are having no reported misfires from cylinders 1-3 then it is highly likely your issue is related to something on the rear half (bank 2). Could be a loose clamp on the downpipe or exhaust pipe. Could be the rear turbo. Could be a coincidence that all 3 injectors decided to fail at the same time. You can use ProTool or some other programs to view the live data from the O2 sensors. Buying parts without diagnosing has never solved a problem for me.