Correct, the original SkyRadar units used the GDL90, and traffic seems to work when available. The newer units are where they made a change, according to SkyRadar and the "piggy backed traffic". Keep in mind that since this is only an ADS-B Reciever, your traffic will be very limited at best, especially when outside Class B. Your 530 is picking up Transponders, correct, not ADS-B. Also the iFly Traffic is shown when alerted in close proximity, dependend on Collision Settings, not long distance like your 530 or TCAS.
An ADS-B receiver will only pick up from the ground TIS-B station or from an ADS-B out equipped plane. The SkyRadar, even dual band will not give the same coverage of traffic, when outside the Class B or TIS-B broadcast area. ADS-B Traffic is not a complete picture and should not be compared to your 530 or TCAS using transponders. As more aircraft are equipped with ADS-B out (closer to 2020) or your plane is equipped with ADS-B Out, then the traffic picture will be more respectable.
There have also been reports that the TIS-B broadcast signals have be up and down in area. Unfortunately there is no Status page from the FAA to see what is going on. We are in contact with ADS-B makers like SkyRadar, NavWorx, Clarity and others. ADS-B has developed nicely for WX, but is still in it's infancy for Traffic.
With also this said, we are testing the ADS-B with the SkyRadar units as there may be a communication issue or fix needed. Walter will be taking readings from several units, early and newer to see what is going on. More soon.