Hi,
as I was 'porting' my disto patch to Max/msp, I had to figure out what permutation and sign rules could change Puredata biquad filter coefficients into Max/msp [biquad~] coefficients. I found these rules comparing coeffcients given by the excellent [filtercoeff.mmb] made by Maelstorm to those calculated by a 'classic' [filtergraph~] in Max/Msp.
Here are two patches allowing to make this conversion in one direction or the other.
Nau