We found the 30 Hz high pass filters had lower gain than what they used to be at low frequcnies.
So we increased the gain of the high pass filters called '30:0.0' by a factor of 10 to have the same gain as before.
I'm not convinced that this is what you want to do, or at least I wouldn't do it this way. The "k" in the zpk filter was set such that the filter had unity gain above the high-pass cut-off frequency. For a 30 Hz high-pass the k needs to be a factor of 10 smaller than it would be for a 3 Hz high-pass to achieve this high frequency unity gain.
As it is now these HP filters have 20 dB of gain above 30 Hz. If the open loop transfer function needs to more gain I would have done that by adjusting the overall DC gain of the filter bank, not by increasing the gain in this one filter. Maybe you guys have been doing it differently, though. Or maybe I'm just completely off base.