I was browsing for discussions of Yamaha NS speakers and came across this old thread. I have loved NS speakers since 1976 when I bought a pair of NS-670 speakers and paired the with a Luxman L507 integrated amplifier. I loved the sound of them and added a pair of NS-690 speakers to go with them. That was a great sounding system. In 1983 I saved up and splurged on a new system (although I kept my 70's system...still have it). I bought Yamaha C-70, M-70, T1000 and a pair of NS-2000s. I had gone down to a local store to hear the NS-2000s and that did it for me. I still have them and they will likely always be my favorites. I have added a pair of NS-1000M and NS-500M speakers to my Yamaha NS collection. I like their sound but they really don't match what the NS-2000s do. Of course speaker selection is always a very personal thing. That's why, like phono cartridges, there are so many different flavors.
In answer to the question about driving the NS-2000s, my M-70 never had a problem and I used to crank the volume up pretty good. I still have that amplifier but I have added Yamaha's M85 and MX-1000 power amps to my collection. All of the amps had no problems with the NS-2000s. I think the MX-1000s may sound the best though. For me it is hard to beat Yamaha amplifier and speaker components from the 70's and 80's.
-sonavor