I just found out the DSP of Guitarix is done in Faust. So I compiled all *.dsp Files in the source-code as pd-externals using Faust.
I had to fix some dependencies - I just put everything g++ can't find in the "faust"-folder, and did some minor changes to the source code (valve.h and 12ax7.cc):
Every external I tried works. Nearly 200 externals, including amp-simulations, tonestacks, stompbox-fx, a lot of building blocks, ...
I could not figure out how the cabinet-simulation works, though - something with IR I guess. Maybe some objects only make sense inside Guitarix. Some are too demanding for this small cpu.
Here is the library I compiled for Raspberry Pi. ( from the LV2 source code ):
example helpfile included.
Have fun to try these things and please let me know if you have some hints on how to put the building-blocks in a meaningful order