What makes the NS2 special, aside from those absolutely stunning glossy finishes and lovely figured maple tops, is the HAZ which has such a unique tone signature. Good luck, OP.
I agree that these bass guitars have stunning glossy finishes and lovely figured maple tops but, I dsagree with the opinion the HAZ would have a "unique tone signature".
I have got both, an US spector NS-2O (with the HAZ inside ) and also an EU spector NS4-CRFM (with a EMG BTS 2 band EQ control).
Although both bass guitars are nearly of just the same design of construction, regarding body wood (full maple wings) and the neck (three stripes of maple) and also the bridge, whenever the instrument is played unplugged from an amplifier then the basic (unpluged) sound of each instrument is noticeable different to each other.
The difference may be mainly caused by the fretboard and its different wood. Pau Ferro wood for the fretboard of the NS-2O and at the other side Rosewood for the EU spector.
Some years ago I played a US NS2 in a music store that had an Aguilar 2 band EQ inside. When plugged into an amplifier this "special" NS2 pushed out just the same unique spector growl as if it was a HAZ inside, but it was not!
For my NS-2O I can tell that the US spector growl is there even with the (HAZ-)EQ knobs in flat position. And even if I would fully bypass the HAZ the instrument would push out its "naturally given" spector growl.
I could even swap the HAZ for a EMG BTS and the unique spector growl would still remain, even with the BTS.
I have got a HAZ clone here in spare that I could any time install into my EU spector, but I don't. And as far as I can tell there wasn't any benefit "soundwise" if I would do it.
The BTS control fits soundwise very well to the basic sound of the instrument that is anyway a little bit snappy. If I would install the HAZ clone then the sound would become even more snappy than already is. .
The basic sound of my NS-2O is a lil more to the "mellow side" if both instruments are directly compared each other, thus the somewhat more "agressive" trebel control of the HAZ fits for sure way better to the NS-2O rather than to my "snappy like" EU spector.
The archive of the classifieds is full with sold EU spectors that are upgraded with the US HAZ or at least with one of its clones.
It makes me very very wondering WHY so many spectors are frequently offered for cheap, and all of them pretended to be really "truly" as close as possible to an US spector.
Personally I think that most part of all these sellers had experineced the hard and expensive way that the HAZ can't transform a EU spector into an US like spector.
Very likely the shot backfired soundwise with the HAZ upgrade, and in the end these instruments are all sold cause they still remain what they are, EU spectors with a distinct "unique" sound!