I would suggest that you consider improving your power first, which will open up many more choices on speakers. Much of the high-end stuff we talk about here is fairly inefficient.
My recommendation would be to look for an amp that can push 100 watts per channel minimum, and use your NAD as a preamp (I'm pretty sure you have pre-outs) so you don't lose your investment.
Once that's done, if you're willing to look at pre-owned gear, have a listen on a pair of Dahlquist DQ10s. They can be had for under $500 a set in excellent condition, are easily maintained and are still to this day considered a terrific value. They are, however, highly inefficient. ;-(
