Ok, I cleared my mind.
Of course two biquad filters combine in series or in parallel resulting in a FOURTH order recursive filter.
So the only mean of doing this by coefficient calculation (following http://www.dspguide.com/CH19.PDF , pages 617-618) is to create such a recursive filter in Pd. I could try to make such an abstraction with [cpole~] and [czero~] objects, but this requires solving a fourth order equation (far from trivial for me).
I love learning, but priority for this idea will be deffered to 'low', till I find a library that does the math for me. Furthemore, I don't know if this will give better results. And maybe there's another way, manual recursion equation ?
But Maelstorm's proposal of a simple [hip~5] is perfect, as this remembered me that in the original design the emitter-follower stages can be seen as [hip~ 3], one at the input and the other at the output ! In fact as I mentionned before I tend to find this disto rather acid, and I stupidly removed those filters to 'save the bass', and rapidly forgot this 'cut' in the circuit. Of course in an analog circuitry this has a 'protection' function, which I dumbly decided to consider 'unuseful' for a digital design. Doh.
Thank you,
Nau