So, to reconfirm, the "modify playlists" comment I make is strictly talking about what I can do on the r3 itself, not accessing the r3's playlists from a computer.
And unfortunately, when editing playlists on the r3, I can't set song order manually on the r3 or r6. Or, more accurately, if there is a way, I don't know how. By "modify" I only meant adding and deleting songs from the playlists.
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But, even if I could modify the song order manually right on r3 or r6, it's still very very cumbersome for me. Really, I wish there was a super fast and easy way to automate or simplify making playlists from my Mac or import playlists created by Cantata (my directory structure is identical on all my sd cards)