perhaps the FAQ entry should mention that playlist insert/append/replace works with a long-press of Menu on the Rio remote?

It does. I quote directly from that FAQ entry:

"Note that the Menu/OK button on the Rio Remote also works for this trick (you can press and hold it). The Kenwood remote does not work for this trick, though, since its DNPP button doesn't have a "hold" option."
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Tony Fabris