I have owned the CA 640C v1 and now own the CA 640C v2. Several key improvements including better power supply and two DACs instead of one make the version 2 significantly better than the original in terms of smoothness, timing, resolution, low level detail and bass definition. I like this player very much FOR THE COST. Other players in this price range have different strengths, but none can touch this one in terms of information recovery. I think it raised the bar for this price point when it came out, and CA seems to be on an aggressive upgrade and product development path.
With that said, both of the 640C v1 and v2 are on the forward side of neutral and sacrifice some overall depth and width of the soundstage in favor of resolution and instrument placement. Neither one should be considered in the league with $1-$2K players, new or used, and to do so would be a joke.
Back to the original point of the thread, the 840C is a completely different animal with better DACs and other parts, very sophisticated processing algorithms and upsampling. I have heard the 840C briefly and was impressed. While the build quality on the 640C is high for it's price range - essentially the same level of finish on the $1400 840C is only ordinary, but "look" with your ears first.
In addition to the other players mentioned in the thread above, I would offer honorable mention to the NAD M5 CD SACD player. I have only heard the Simaudio CD1 once and can't offer a well developed opinion on that yet - I would say it sounded very neutral and pleasant. I have not heard the Marantz SA8001 but it is suppose to be a lot of player for the money (<$900).
My current Top 5 list between $1-$2K based on personal experience and reviews by others would be in no particular order:
-Naim CD5i
-Rega Apollo
-Cambridge Audio 840C
-Underwood HiFi Mini mod Shanling CD 3000 (or other Shanling)
-Musical Fidelity A5 (used).