Pioneer VS43X vs. Yamaha RX2300 vs. Onkyo TNSR800

Actually, Yamaha has a pretty good rep when it comes to surround sound units. And many have accommodations for 4 ohms drive capacity with the switching on the back. To say all yamaha units are "Junk" is pretty harsh and ill-informed, take a look in any number of audio mags.

Wrong Emery, I have the Yamaha and it has a switch to change speaker impedance to 4/6 ohm

MA

Personally, I would go with Denon, Marantz or Outlaw. The sony is difficult to use (I hate the remote), the yamaha is junk compared to the others, Onkyo makes better units, the pioneer is very nice but may not be able to handle the power requirements.
NHT are not easy to drive (but sound great). Most theater receivers are not rated below 8ohm speakers (especially yamaha). Check to see if they can drive the NHT. Also, due to the NHT's lack of efficiency, you will be working these amps hard and may blow the reciever.

Good luck,
Emery