Congratulations for your successful mounting! Well done!
And thanks for the demo video and your kind words, althought the true is that i'm quite clumsy and moony
Regarding your question about the ZynAddSubFX and the complex pads, i'm sorry to tell you that there is no solution by now. The RBPI3's CPU/FPU (ARM Cortex-A53 QuadCore at 1.2 GHz) is not powerful enough. You can try to "overclock" a little bit the CPU, but the improvement is little.
The problem is that ZynAddSubFX only can use a single core and it's very difficult to paralelize the code because of its nature. Also, i suspect that the memory<=>CPU speed can be a limiting factor here, due to the intensive use of precalculated tables, specially with the unique PAD synth algorithm implemented in ZynAddSubFX.
So, right now it's very difficult to overcome the limitations with this presets. Our best chance is waiting for the RBPi4