Best speakers under $500? Fire away!

Greetings, Have you tried the Marimbas' from Music Hall?  Musical with Pretty decent reviews and reasonable prices.  They are 6ohm and 87db efficient, so your receiver may work with these.  Talk to/ask the experts (which isn't me), all I know is that they sound good. 
Good luck...

You you might try the Emotive Airmotiv 4s active speakers and just use the preamp out on your NAD 3020. Each speaker is bi-amped with a 25 watt amp driving the air motion ribbon tweeter and and another 25 watt amp driving the woofer. The price on these speakers I believe is $299 for a pair direct from the manufacture. The received a good review in Stereophile and have a C class rating although one of the reviewers thought it to be class B. Plan on getting some good interconnects to hook the up to your preamp. I'm using Kimber Cable "Hero's" on my Airmotiv 4s' so that will bring you to your $500 give or take any deal you get on the interconnects.

I had paired Jolida 502 int amp with Totem Rainmakers for several years for 2 channel music in my home office. I got a pair of Monitor  Audio Bronze 2 for about $350 on sale to use for front wide in my theater. I hooked MA2 to Jolida just to test but what a surprizpse. MA 2s were as good as Rainmakers. 

Dealer disclaimer

Elac UB5 is unbeatable at $499/pair astonishing speaker that somehow does it all.  Magic.

Another vote for JBL Studio 530. Compression driver is super smooth.