The tmcc base would be able to receive commands if the data driver was not loading the Legacy base down as it does and as we all (almost all) have been saying over and over.
So when you put the data driver back on the tmcc base, the tmcc base is not loaded down beyond its capabilities like the Legacy base, so it can drive lots of stuff (like Z stuff

Have a wine cooler break at this point...
Not a wire, but add a booster amp to the Legacy base, and then plug in the driver card to it.
Again, if Lionel did not change the base output to be compatible with a PC, and had kept the tmcc base output circuit, then this would have been a cake walk too. BUT, the future Legacy developments are worth a little thoughtful change.
Get the amp. Just remember to split off the connection to the computer with a Y cable and plug in the booster amp to the other connection of the Y.