Quick note about WinISD and boost. WinISD appears to assume that the amp being used can provide the necessary power to cover the boost above the value on the input tab. Meaning, if you enter 100 watts on the input tab, but apply +3dB of boost in the EQ tab...your excursion graphs will correspond to the same alignment with no boost and 200 watts...+3db = 2*power.
I haven't looked at Blue's project file, but if it's got +6dB dialed in with a 240 watt input, WinISD is actually simulating the excursion graphs with 960 watts at 35hz. Reading Mike's summary, sounds like excursion limited power is around 400 watts...100 watts with +6dB = 400 or 208 with +3dB = 416.
Blue, if you've dialed +6dB into a 240 watt amp, but the driver and
PR have the excursion to handle 400ish watts, then it is likely that the popping you're hearing could be the amp clipping since the input signal could be calling for more output than the amp has to give after the boost is applied. I don't have a BFD, but if it has clipping indicators for the line level signal as you describe, that could probably produce a popping signal if a clipped signal was sent to the amp...somehow you'd need to reduce the signal level before the BFD.
And this all may be nonsense rambling on my part...quick reading and replying when I should already be asleep could be dangerous.
-Brent