IIUC, filters F1 and F3 should have flat amplitude and phase response up to 20KHz (with differing responses above 20K ofc). The rest of the filters (except for the “dispertion” filter perhaps??) do things to the signal that may be audible.
Amplitude looks more or less same but phase doesn't in a simple loop back test, now below example is not AKM brand but a ESS example and will guess scheme will be the same for AKM if measured. When using pure minimum phase filter that is so steep it looks phase distortion creep in compared to nature of a minimum phase domain showed overlaid in grey color trace.