Hi,

The communication between the 430 and the 296 is one way only, from the
430 (or 530) to the 296.

That is true, but I never asked about that connection!
The connection I am talking about is the so called Crossfill and is used
to connect two similar units: 430-430, 430-530, 530-530 and it does
allow to send all the waypoints (as well as routes) between units.

There exists no way to program a flight plan at home and then transfer
it to the 430 (or 530).

That is the "official" Garmin position. But since Crossfill alows that,
it is posible to "sniff" a Crossfill between two units and reproduce it
on a PC. In that case the PC simulates to be a 430 that simply wants to
send waypoints to the real one.

That is for sure feasible, the only problem is that the protocol is not
documented yet (but remember the handheld protocol was not delivered by
Garmin until people cracked it... now it freely available on their site)
and I have currently not two units to be placed on a bank to look inside
the dialogue!

Giuliano