Tubes4Hifi offers the VTA amps in kit or complete. These are power amps, not integrated amps, so would require a separate preamp unless your NAD has pre-out capability.
I added the VTA mods to my pair of Dyna 70s about 3 years ago, and have been extremely pleased, and feel I'd be remiss for not mentioning them. I also listen primarily to folk rock, jazz, male/female vocals, and find that they drive my 89db sensitivity speakers nice in even in a large room. A completed VTA 70 (35wpc) is just about within budget, and is definitely within reach if you're willing to solder.
Either way, I hope you find the same magical midrange that many tube lovers do.