Hello
The PX is an amazing synth. If you ignore the sample features, it is pretty much a conventional analog synth (but with digital oscillators for stability), so any analog synthesis tutorial that takes you through the conventional signal flow of oscillators, filters, amplifiers, envelope generators, low frequency oscillators and other modifiers, will get you going
Once you are familiar with that, then the sample capabilities can be mastered, but these can be essentially thought of as alternate oscillators