We already had a small chat about this nice project via my other account ('Ernie Fendelbin', that I had to discontinue).
After testing with an Arduino Uno, I now switched (via a Mega) to a Due and created a display (with its own Nano, or Uno) to monitor all inputs, counters and outputs.
I've also mimiced the ftDuino hardware for the input with an 4051D and added two TB6612FNG for the outputs. In other words... I now turn out to be building my own ftDuino, haha. But with other motor drivers and as an 'Due-shield' and external display so to speak.
So next step is to interpretate and handle the in-/output configuration send by the TXT. So I've added the TA_CONFIG struct to fx1.h and now have to expand your fx1ParserParse() function.
Just to be sure: these are the command 'codes' in the document 'Robo-TX-RS-485-Protokoll.pdf', that is based on the 'ROBO_TX_FW.h'? Or is there already more in depth documentation of the 'Fish.X1'-protocol available?
First I'll study your fx1ParserParse() function a bit more... to be continued

Cheers, Arnoud