In my opinion, the Thumb NT 5 is THE best sounding Thumb because of the pickup placement, as the pickups are closer to the bridge, and because of the Bubinga. The 4 and 6 string versions have slightly different pickup placements (less close to the bridge) which yield a slightly less aggressive tone. Therefore, below is my input in their respective order of importance (according to my experience).
1) The first and foremost thing to getting close to the Thumb tone is to emulate the Thumb 5's pickup placement.
2) You will want to use in-line split-coil pickups just like the MECs on the Thumb NT (or find a pair of used MEC pickups here on TB or eBay). Barts are a popular choice but they tend to be warmer and tamer. The MECs are the more original choice because they are brighter and have a "bouncier" tone, at least to my ears.
3) Pair the pickups with a 3-band preamp. Mids are an integral part of the equation.
4) The Thumb NT is mainly made out of Bubinga. Bubinga is a fairly bright-sounding wood. Therefore, even if you use a bass made mostly out of maple, you will get very close to a Thumb NT sound.
Does the aggressiveness come mostly from the pickup placement on the 5?
A 6 string bolt on Bubinga with 2 band EQ would be:
1. less aggressive.
2. less sustain.
3. due to the 2 band, getting that 5 string mid growl would be difficult.
There are a bunch of 6 string Bubinga and Wenge combo with 2 bands on sale. But as some others have noted, 2 band eq just might not cut it.....
