Please disregard my previous post, GeoFlute with Sylphyo does work! :-)
If you want to know how and are not interested in my continuing ramble, please go to the end.
I was determined to get GeoFlute working.
So since I already have Audiobus on my iPhone, I bought a MIDI converter, mfxConvert, with the aim of converting Aftertouch to Channel Pressure.
Activating the converter in learning mode, I discovered that the Aftertouch of the Sylphyo is really sending MPE Channel Pressure all along!
So what gives?
In the end the problem was really simple. GeoFlute only starts from C4 and covers 3 octaves. So simple that it initially didn't occur to me. I had been spoiled by the 5+ octaves of the Sylphyo. :-)
Once I started playing above C4, the result was spectacular. It is the closest sound I have gotten with my Sylphyo to my real flute up to now. I am amazed that a iPhone 6S can generate such a realistic sound. I still have to learn how to control the sound better but I am very optimistic.
I am not sure if some of the other CCs from the Sylpho will need to be remapped from channel 2 to channel 1 to conform to the MPE spec but I have mfxConvert if I need to.
Maybe @Support_AODYO can add a MPE output option in the future and save all this hassle?
So, in short, to start playing GeoFlute with Sylphyo, set Sylphyo breath control to Aftertouch, Sylphyo MIDI channel to 2, Sylphyo base note at C4 and the GeoShred MIDI to SWAM. I also recommend that the Echo and Reverb of the GeoFlute be turned off, at least at first.