A case of "all's well that ends well":
Thanks to an old post from 2013, I was able to get my Legacy system working without another trip to Lionel!
The long story is: that I received my Legacy controller and base back from Lionel today after they made the following repairs:
"Installed charging upgrade; replaced a "bad" component; updated software to v1.60; tested range, serial, and charging circuit."
"Replaced remote PCB and LDC screens (display / liquid crystal, touchpad liquid crystal and PCB) all in the Legacy remote."
I had returned the system under their very extended warranty program for the well known charging issue as well as an issue where new alkaline batteries were dead the next morning with the Cab2 turned off.
The happy ending, thanks to the 2013 forum post is that when I received the Legacy units back from Lionel, I got the "Legacy Error: Cannot Find Base". After multiple tries at scanning for the base, I decided to do a search and came to the 2013 forum post that suggested re-loading the base and handheld software files when this situation was found in newly purchased Legacy systems.
Using the Legacy system utility, I was able to get the v6.0 files on the black modules and loaded to the base and remote and WOW, after that I was connected!
Of course I should not have expected to need to go that route after getting the system back from Lionel service, but on the other hand I am still thrilled that Lionel has extended the warranty to the system and very glad that I got the GREAT advice from this forum!
Now I can return the Cab 1 with original TMCC base that I borrowed from my Grandson that I used while my Legacy system was at Lionel. I built and designed his layout to be able to flip a toggle switch between TMCC and conventional, so he was able to still run trains in conventional mode. My grandson will receive a nice present together with his Cab1 when I give it back to him tomorrow!