I have worked with the plus version quite a bit and here are some things i have come across.
-there is a button in song mode for patterns on the a deck or b deck or both.
the problem with this is: it plays deck a first then deck b. it's basically like having two ds lites synced up and having one muted while the other plays.
-if you have a song where both patterns need to be played at the same time from different decks you would have to upload the file to another ds or dsi to play at the same time.
-the track mutes work wonders for composing on the song mode.
-when recording out of the dsi you have to record your decks separately and combine the tracks in a daw.
-when you stop a song in song mode and go back to pattern mode the tracks that are muted in the song at that point will be muted in that pattern. you will need to go the mixer to clear the muted tracks.
please correct me if i am missing something with the decks. i will post on the patterns and how the decks react soon.