How to add DCC to the new run of Bachmann DCC ready Dash 8-40CW?
The current recommendation is for direct soldering, using either DZ125, which controls headlights only or DZ143, which controls headlight and two additional functions.
With earlier units, either milling of the frame or a replacement frame was necessary, but the new units have a "DCC ready frame"; the source of this information also points out that Bachmann is using the same model number for both the older version and the newer version, so you should make certain that you have the recent version.