according to the software update 4.0 the gxm 40 is now supported. a garmin tech says it's only a traffic receiver antenna not a xm antenna. they seem to have to look everything up btw ...... so you can't have both xm weather and traffic together ? that doesn't sound right at all. I don't think the tech knew what he was talking about?!
Garmin GPSMAP 640 (this is the chartplotter that uses the gxm40)
the garmin XM page:
I also asked about the gxm31 and if that would work with the 478 and the garmin tech said it would if I was to make an adapter connector. (i might be able to get one of these cheap)
note: there also another antenna listed that will work
GA 26C low-profile remote automobile antenna
presently I'm downloading the 2010 map updates, I'm 73 % done ..... no problems so far ...
I also ordered 2 otterboxes, one clear, one black, and will try to swap covers so I can have a clear cover on the black box. Hopefully the clear cover will be clear enough to see the gps screen ......