FYI this was also covered over here https://ogrforum.ogaugerr.com/...2#149943328429214392
This post by @MartyE
Also, to get full legacy- must be a Lionel Legacy or new CAB3 base, and the all important Lionel LCS module SER2 (and also a PDI cable and possibly power system depending on base), and the MTH serial data cable 50-1032, along with also requiring the premium DCS app license.
Both sides are a little guilty on the "what extra bits are required". Again, for whatever reason, Lionel made it such that you need a SER2 to perform some level of translation of the commands to actually get full legacy functionality for the original 990 Legacy base. Then on CAB3 base, you need a SER2 because there is no native serial port. The main difference being the 990 Legacy base install and SER2 needs the PDI starter Y cable that includes the PDI power adapter because the Legacy base serial port does not supply any power for the LCS modules. The Base3 install, the base has powered PDI ports built in to power LCS modules, but no serial port, so you need a normal PDI cable and LCS SER2 to give the Base3 a serial port.
On the MTH side, while in theory serial is serial- the 50-1032 cable has some buffering and level translation to ensure compatibility with Lionel and other products. And then the need for the Premium DCS app license "upgrade" that unlocks the greyed out features in the app.
