If you are looking for a bookshelf speaker, allow me to recommend the Yamaha NX-E100 bookshelf speaker which was bundled with the E100 mini-system. These speakers are not cheap throwaway consumer crap, Yamaha put some effort into them. They have the same family sound as classic NS from the Seventies and Eighties which is crystal clear clarity and transparency. Like the great NS speakers of yore, the NX-E100 thrives with fast, objectively accurate amps but unlike some NS, does not punish receivers. The best news is they are common, relatively cheap on ebay, and sometimes dirt cheap at the thrifts. The NX-E100 has a cloth dome tweeter so I would place the sound close to the NS-670 and NS-200M. I am not a fan of three way speakers which to me sound a little incoherent, something the two way NX-E100 avoids. Balance is excellent. The Beryllium dome NS-500M and 1000M are different animals and with the right amp and recording, are in a different league. However, they do not suffer fools which is where the NX-E100 scores. Cloth dome tweeters are much more forgiving which means a wider variety of gear and recordings can be played. Cloth domes are almost as transparent as Be domes perhaps giving up a little with metal strings and horns. My older ears use to crave the edginess of Be but no more, cloth domes hit the sweet spot.