I have a pair of both the CM9 and 683 speakers. The CM9s are doing duty as the mains and the 683s are the rears. Overall, I like both speakers.
I felt the 683s lacked a true lower end punch, so I upgraded by adding in a JL F112 sub. This gave movies a real wow factor and worked very nicely for music. I have never spent much time listening to the CM9s without the sub handling frequencies under 80Hz.
I would like to point out some differences between these two speakers. The 683s are brighter which some might say sparkle. The CM9s are more relaxed sounding. The two speakers do sound different but the mid and highs are not dramatically different. Using them both for movies, they blind nicely.
The 683s have a smaller sound stage. At times the sound felt pointed. With a lot of setup and testing, I was able to find a sweet spot for our listening position with a good balance of energy and stage. The CM9s are very different in the sound stage and presentation. They do a better job filling a much larger area. They required less setup and fiddling with toe-in. I found the 683s incredible sensitive to toe-in to get the best sound possible.
Some things to consider are the ports. The 683 has a front port and the CM9 faces the rear. You need to consider this in planning the placement. I found the CM9s to perform much better a little distance away from the wall. If you have to place them flush, the 683s might be the better choice. Also consider the space you are trying to fill.
