I can attest that. The problem with the fat stacks is that it's noticeaby louder in single-coil mode, I'm guessing that's why they suggest a preamp - to compensate the volume loss switching from single-coil mode to stacked mode. Otherwise in stacked mode it competes just as well with -say- Aeros I have loudnesswise.All the Nord pups work wonderfully passive... no doubt on this!
On a side note; IMHO after the release of Big Splits, Fat Stacks are kinda moot now. Big Splits have all the boldness of Fat stacks in single-coil mode but without hum. To emulate the stacked mode all you need to do is to roll off highs a little bit.

