ISTR that somebody wanted +/-9dB range, and somebody else wanted 0.5dB resolution. Can't win

I'd recommend starting by duplicating the existing range though. It's hard to say what values to use though - the existing EQ fudge is based upon center frequencies and Q factors, whereas the DSP algorithm is based on cutoff frequencies and order (2nd or 3rd IIRC). But I think off the top of my head that a 2nd order at the listed values should be a reasonable approximation to the existing controls. Let me check...