As far as I know, a lot of those devices use media transfer protocol (MTP) to communicate with the computer. In this case, there isn't really a way of using foobar2000 to transfer music across. Of course, you can see if I'm wrong by finding out whether or not the device has a drive letter in Windows Explorer. If it does, then you'll be in luck.
However i want to be able to copy foobar playlists across and have it automatically take over the songs and the playlist - is this possible?