An additional CC as indicator for the Roll direction left/right is not the best idea. Selectable CCs for left/right would be the way to go. Set them to the same value: play as usual. Set them different: You get one for Roll left and one for Roll right. Same for Compass.
@peter-ostry These are placeholders! You can use them as you would the normal sounds or you can just ignore them. They get progressively replaced as we add new sounds to the Sylphyo and are essentially there to fill the empty slots. It can also be convenient when for example switching from sound 34 back to sound 1, you can just switch over to sound 36 instead.
Checked again and disabled the Sylphyo's movement CCs. Really cannot tell what is going on. Stuck notes, changing/losing the Sylphyo's internal sound (I mix with the Link's stereo input) and weird behavior overall. Turned everything off and on in different order – no change. Turned everything off, went back to direct MIDI connection and it worked fine.
Never mind. I believe some devilish ghost in a parallel universe prevents me from using USB hosts. A Keith McMillen host did not work here. A Kenton USB host didn't. Why should the Link do. I blame the ghost ;-)