Rick,
looks like Garmin has backported to both the 196 and 296 the same features who first appeared on the 396, as far as interfacing with an SL30 radio. I have a 296 but was unaware they had done the same for the 196 users.
What happens with the SL30 when connected to an x96 unit is this. First of all, the GPS knows where it is (doh!) and will compare the current position to the VOR database, and send out to the SL30 the frequencies and IDs of the 10 nearest VOR station, so that they are preloaded in the SL30. It will then be very easy to tune the required VOR station, and let the SL30 do the morse code identifcation...
For the COM part, if an airport is either the current position or the next waypoint, the GPS will preload all the COM frequencies in the radio, allowing for a quick selection of the required frequency. You can also force tuning a frequency from the airport information page (getting there for instance from the nearby airports page) and hit ENTER to send the frequency to the SL30.
All this happens at 9600 bps, with proprietary UPSat/Apollo/Garmin NMEA sentences, interleaved with the normal NMEA data, all this having selected "Aviation In/NMEA & VHF Out" on an available COM port.
I have yet to see this at work, as I will be getting my SL30 in a couple of months time, hopefully, but I have gathered all the information I gave you by decoding the NMEA stream and understanding the rationale behind it... quite nice, I have to say... if only the x96 could display an HSI+LOC/GS on the screen when tuned to an VOR or ILS...
Let me know if this clarifies things.
Ciao, Luca