Thanks for your reply. Add-only syncing won't work for me.
I think I'll keep using MediaMonkey and hope for the day when it can recognize an expansion card in the player (currently a known limitation). Actually I just today discovered a very useful feature in MediaMonkey; the ability to create an auto-playlist that doesn't include the files in another auto-playlist. So I can sync my Connect's internal memory separately from the expansion card and know that the two won't contain the same songs. Really nice. As soon as I can do this without having to take the card out of the player, I'll really be rockin'.