How to draw the magnitude plot of a variable slope low/high pass shelving filter? (eg. as a function of cascaded shelving filters)
If you can generate a grey noise signal to put through the filter, the amplitude can be plotted as the resulting graph. Also if you pitche a sine input to the function at every frequency that you wish to measure for, the sine's amplitude after the filter will be the result for every frequency.

I understand that i in this graph is the audio sample instance...

*c[i] = cutoffHz * 2^((((135-cutoffPitch)/12) / numberBands) * i)*

Then send sines through it at every of the 16 bands of the EQ and check the resulting maximum, i.e. from a loop of sines of 10 periods of samples at 16 frequencies. perhaps you have to fade the sine amplitude into the filter to avoid an artefact.