A real statement loudspeaker, Yamaha touted that it was "the end of the weak link"... NS stands for Natural Sound, Yamaha's top-end series, still online today, but perhaps with less stringent specs. M stands for Monitor, maturally.
The NS-1000 is the "home" version, adorned with a lavish bony/polyurethane finish and no a veneer add-on, mind you but real solid thick wood! Apart from this 8kg surplus of good looks and the protecion on the woofer of the "M", both versions are identical.