They are both very good but very different sounding from each other. With CD players, people often look at the digital aspects of the player but overlook the analog section. Thats really the big difference. With the Ayre, you get an analog section that matches the sound and build quality of their other components. The sound is very detailed but clean and pure. Imaging and dynamic contrast is exceptional, as well. The downside is that it is not the most forgiving CD player out there. It reveals what is on the disc, good or bad. Personally, it would be my first choice if I was looking for something in that price range.
The Cambridge is also very good player. It does sacrifice some of the things that the Ayre does well in trade for a more forgiving sound. You really need to listen to both of them. If you've ever heard a Wadia and liked it, the Ayre is the way to go. If you've ever heard something from Arcam like an FMJ 33 or 36, and thought that was good, the Cambridge may be a better choice. Actually, if you can find a good used 33, it might be a better choice than the 840. I have one myself and find it to be a great player all around.
The Cambridge is also very good player. It does sacrifice some of the things that the Ayre does well in trade for a more forgiving sound. You really need to listen to both of them. If you've ever heard a Wadia and liked it, the Ayre is the way to go. If you've ever heard something from Arcam like an FMJ 33 or 36, and thought that was good, the Cambridge may be a better choice. Actually, if you can find a good used 33, it might be a better choice than the 840. I have one myself and find it to be a great player all around.