That number is for a single Nu pickup. It will be more when combined and mixed to mono with a mixer. So for 6 channels, that's an additional 15dB.
Hum is not an issue with the Nu. Low impedance coils are a lot less susceptible to noise. The more important issue is hiss (broadband noise) introduced by the active electronics (the preamplifier), and so that one has to be very quiet (hence using that toshiba ultra low noise transistors was a crucial design decision). Take note that the hiss is higher than the active EMG 81 by around 5-6dB. The reason is because the preamp had to push the gain more than the EMGs which has higher output from the coils to begin with. The EMG's preamp gain is 3 while the Nu requires at least 10.
Yet, this hiss is so much well below the hum and is not perceptible at all, ... until you push the gain. That's the real battle. Unlike mics, guitar pickups are in a precarious place in the signal path since it sits at the very beginning before high gain stages (compressors, distortions, overdrives, preamps, etc. which can push the gain to such horrific :-) levels). So my recommendation for really high gain is 1. Use a pre-filter per channel at around 2-6kHz (high gain distortions do not like the full spectrum anyway -- the high frequency intermodulations are nasty beasts) and 2. Use a noise gate, or a gentle downward expander set above the noise threshold, on each channel. The gates also help a lot in cleaning up channel crosstalk when doing polyphonic distortion.