Port 2 has not ever worked (regardless of whether it was configured as 232 or wifi)...supposed to be a fix in 5.0(don't hold your breath).
Getting the three Green Ready for flight indicates that you are getting position from your 480 while getting squawk and altitude from your SL-70. What baud rate are you running the SL-70 at and is it configured in the NavWorx box as SL-70R? The reason I ask this question specifically is from my installation, the SL-70R configuration (Extended output and 9600baud) is the only one that will receive changes to the squawk code from the transponder. I had been working with NavWorx on this issue prior to them shuttering operations...running the transponder at 9600Baud prohibits it from communicating altitude data to my MX-20 - I'm working around that by replacing my Alt Encoder with a serial capable ACK A30.9.
I have the MX-20 instead of the GMX200 - but they should be similar... My MX-20 is configured to receive GDL90 UAT Radio on port 4. Are you using both the transmit and receive 422 pairs? I would ring out the wiring for the GMX200 - ADS600B interconnect...at one point I had one itty-bitty shield wire touching one of my signal wires and it went intermittent on me.
With the exception of the ADS600B/SL-70/MX20 interoperability mismatch, mine works well - I get traffic and weather on my MX-20 and traffic on my 430W.
Ralph E. Capen
RV6AQB N822AR @ N06