Is this the original Tone Monster from GN1? How are the active circuits arranges in relation to the switching?
With that kind of series/parallel wiring, any active circuits would need to go after the switching, so that the switching is just on the passive coils, with the output then going into the active circuit. I dont know if that is possible with EMGs
If your using EMG active PU's (the one's w/ the battery), you're going to have issues especially if you're using just one battery and series modes.
The only way that this might work is if you use a separate battery for each PU (and then there will be issues if you have any post-processing active modules like the SPC that might share any of the batteries).
One of the neat things about passive PU's is that their electrical characteristics interact. Two in series are darker due to the combined inductance (A+B) and two in parallel are brighter, again due to the combined inductance (A*B/(A+B)).
Since EMG active PU's have an internal OPAMP w/ a 10K output resistance (they call it impedance), the tonal benefits of series vs parallel are somewhat lost (no LC interactions), and only relative loudness will prevail. EMG active's are already plenty hot. The 10K (OK, some) output resistance is required to allow the PU's to be parallel mixed.
I have a DG20 set (3 SA's) and in the "notch" positions, while you can hear the disparate string position detection from 2 PU's, there ain't no "quack" 'cuz there ain't no LC interaction. I hated them and they came out immediately.
(If your interested, I do have a circuit idea on how to effect a tone response similar to "quack" in the "notch" positions.)
But, I tend to believe that series is quite moot w/ EMG actives (and possibly quite "pop"ular).