Whare are the key differences for the TAZ 6 between those two versions?
You can read up on the full stats of the board here: https://ultimachine.com/products/rambo-1-4
From the article however:
RAMBo v1.4 - The major difference over the previous version is the integrated LCD connector for Smart LCD Controllers. The EXT2 and SPI headers were re-arranged to remove the need for an adapter. This change is backwards compatible with firmware for previous versions of Rambo that normally utilize the RamboLCD.
Essentially Ultimaker reved the Rambo board during our production run, and we started using the latest and greatest. We hope this helps!