Preamp w/ a budget of $2000

If you can find one, a Bryston BP6 fits your description perfectly.  I've had mine for six years.  Straight wire with gain in spades.  Deep holographic and transparent soundstage with pinpoint imaging.  Best of luck. 

I have a Bryston BP6 too, it is what mofojo says.
Bought it on here about 5 years ago for $1200 bucks, use in bedroom system, has nice headphone amp as well.

I also have a Van Alstine Vision pre , all Class A , that sells for  $899
new without remote . Bught new last year .Can be had with superb Van Alstine phono pre for extra $329 , 299$ for remote (I don't like remotes myself.)
It sounds more musical than the BP6 and has an even better headphone amp. Drives  my Senn 650's like a champ which is not easy to do.
BP6 is a tad more quite perhaps but that's about it . AVA is best buy on market and sounds great !  Oh, and it has a built in gain-control (low, high) which is very useful to match up with an amp or speaker .

VTA - http://tubes4hifi.com/

They sell everything both in kit form and preassembled.  Their top line line stage preamp, the SP14 sells for $1350 preassembled and for $960 in kit form.  Their best phono preamp sells for $895 preassembled and for $650 in kit form.

There's a used VTA SP14 selling for $800 at the US Audiomart website.

http://www.usaudiomart.com/details/649355979-tube4hifi-sp15-tube-preamp/

A CJ Classic 2 SE w/Teflon caps selling at Spearit Sound for $1999.

OP, coincidentally I have the same preamp and was/am in the same quest as you are. The usual popular choice in preamp upgrade path is Conrad Johnson and I watch the classifieds and read as much as I could to find a good choice. I had the opportunity to borrow a CJ Classic 2 (not SE) from a friend and used it for two weeks. Even though initially I really liked the CJ lush sound, at the end, even to my own surprise, I much preferred the NAD. I found it more balanced and seemed to cover a much broader range, top and bottom in particular. I have no doubt the higher model CJ preamps or even the SE model(s) sound better but don’t discount how good this particular NAD preamp sounds. And yes, it does run hot and I assumed it had to do with its Class A gain stage. All I’m saying is try to listen to your options if you can before dumping the NAD, especially if you want detail and prefer a more "clinical" sound. Ironically, I was looking for something with a less clinical sound but realized clinical and balanced kind of go together, at least to my ears. Of course the equipment synergy also needs to be considered and maybe in my system this preamp just sounds better than a comparably priced tube replacement.