Is that Arduino Nano on the CrossfirePro board running as the THC?
Probably, they would need some sophisticated digital signal processing capability for that task 
Where did you see a photo that showed that?
Yeah, Nano without the USB connector (or UART probably) . Good catch! However, there are a few other components on that board that probably perform something other than driving the stepper motor…
However, now that I think about it, THC is the only Option on that board and it’s the Nano that’s pluggable… hmmmmm.
Exactly my thinking also.
… Time to start writing some code! 
Further confirmation, it appears to be ‘almost’ a Nano, but LS customized.
The VIM module does all the analog signal processing/filtering, but the ‘Nano’ does the THC logic including ‘Smart Voltage’ processing and Z stepping (at least Up & Down).
Hahahaha!