I have owned 600 series floor standers and currently own CDM-1NTs (stand mounted). Were I faced with your choice, I'd go with the 9NTs. Assuming they're in great shape, you're getting a much nicer speaker all the way around, especially where appearance is concerned. I was able to source replacement tweeters for mine via B&W service center (twin boys as toddlers. . . no surprise) and they were an easy install, so any maintenance you'd need to do should be supported by parts. The sound is more to my preference as well--likely not so much a function of the drivers, but more so because of the enclosure quality.