Yea, there is
I am referencing headers from PD extended. You can find the path in the Xcode Project via the Targets -> syphon.pd_darwin target, Get Info -> Build and then the Header Search Paths, which are currently set to:
"/Applications/Pd-extended.app/Contents/Resources/include"
I also link to GEM.pd_darwin which is also found in the PD-extended app bundle, at :
"/Applications/Pd-extended.app/Contents/Resources/extra/Gem/Gem.pd_darwin"
That ought to be it, the resulting target bundle is set to not require anything else. Unless I am forgetting something 🙂
Basically, install PD-Extended, and you should be ok, and the Xcode project should find what is needed to compile, or hack at the code.
Are you interested in contributing the the PD-GEM / Syphon plugin?