When I was going through the Sound controls in my recently acquired Sansa Fuze+ I found one under Crossfeed, not in the manual, called "Simple (Meier)". This turned out to be the perfect setting for those mid-to-late 60s recordings where the Stereo mixes were appallingly poor, made by sound engineers who had a new toy to play with but hadn't read the instructions. You got songs where there was no soundstaging, but the vocals were in one speaker and the music in the other. Or the drums, bass and rhythm guitar were in one speaker, vocals in both, and lead guitar in the other speaker. They sound really odd through headphones! Switch in "Crossfeed > Simple (Meier)" and whilst the result isn't perfect, at least it's more acceptable.
I wanted to put this as a shortcut, but the necessary setting isn't in Appendix E either. I found it by trying various combinations and it's "crossfeed: meier". I made 3 config files:
stereo.cfg
channels: stereo
crossfeed: off
mono.cfg
channels: mono
crossfeed: off
crossfeed.cfg
channels: stereo
crossfeed: meier
I made them available from shortcuts.txt. Really good choice of stereo effects.