Best speakers under $500? Fire away!

I have as surround a pair of def tech sm 45, just do some research on them, they are very very good

The Monitor Audio Bronze 2 I recommended before is much better than the worfedale 10.1 (9.1 the predecessor was better if you can find one) the Elac is better but less than MA Bronze it can’t matck the strong dynamics of the Bronze I was really overwhelm once I first heard it ,you are buying speaker worth 1K in terms of capability  for $ 400 it’s really a bargain. It’s almost as good as the B&W 685.

seriously, the Gallo CL2's I bought are still breaking in and have detail, accuracy, spaciousness and natural tone that will put many of these suggestions to shame. They are 90db and a transmission line - the bass is extended and accurate, you can actually hear the tone and articulation of the bass, not just boom like the B6. I heard them up against the B&W 685 mentioned above - the Gallos are in a whole different league for sure. That CDT tweeter and crossoverless design is special. Call Dan at Gallo!!!

One other option is a used pair of Tekton Lore Reference - They can be had about $500. Very efficient, huge effortless dynamics and soundstage. 

I see you went with the B6. I think this a mistake based on your amp - they are overly warm, (rolled off really) and very bass heavy (boomy) unless you have a room that is very well treated or can move them into the room about 4 feet, no kidding. I feel like NAD will only exacerbate these issues. B6 would be best match with very accurate and neutral electronics, even on the slightly lean side. good luck.