How does the NavWorx ADS-B out know how to transmit the correct squawk code?  Does it "sniff" the Mode C code then use that to transmit the Mode S ES information?
OK, read the documentation stupid :)   I see now that the NavWorx unit takes an RS-232 feed from the Garmin Mode C transponder which is probably where it is getting its code info.  I also see that the unit requires an external altitude encoder.  It is interesting doing a trade off analysis on a NavWorx versus Trigg solution.