Building on Saki70's comments...the NHT PRO system is just that....two nearfield speakers and a specially designed matched amplifier that allows you to move the boundary...an integrated system designed specifically for your intended use.
You might want to read:
http://mixguides.com/studiomonitors/Reviews/nhtpro-a20-monitor-699/
which describes some of the problems that this type of system can help avoid...and tell you what the A20/A10 might be able to do for you in your environment.
The entire system is also within your price range....and you can keep the SV-236.
I am not sure why you would listen to the classic threes when you are looking for a completely different design point. That's sort of like listening to today's JBL's and saying I don't like any JBL's (and they made some truly outstanding speakers a while back). The NHT Pro has little in common with the NHT Classic Threes other than the company name which has now been sold at least three times since the A20 was offered.
I'm not trying to sell you on the NHT's....there are many solutions. However, I always prefer a total solution rather than putting together individual pieces that each have good reviews and then having to deal with all the integration and room issues that an integrated near field monitor system avoids.