I have a cambridge 640A (I believe is the model). This is the hard drive based system with the previous top of the line CDP integrated into it (at least that is how it was marketed). I use this piece regularly (primarily as a music server). I have listened carefully via its own internal DACs and also via its digital outs going into my Resolution Audio Opus 21 GNSC. The weakness of the Cambridge units (in my opinion) is that the DACs aren't anything special. For my purposes, background music via the hard drive the piece serves my purpose well, very well.
However, if this were my primary CDP, I would be disappointed with it. It is purely an also ran. Not particularly full of life, a little flat in the staging, not overly dynamic. However, keep in mind I am comparing this to much more expensive CDPs that I have run over the past year in my system (Wadia, Audio Aero Prima and Capitole and the Resolution Audio Opus 21 GNSC).
Do I think the Cambridge is bad? No, but I don't think it is special either. I think it is purely an also ran that does not deliver as well as many other similarly priced CDPs and even lesser priced one. Will you hate it? Probably not. Will you love it? Doubtful.
I think you will find that it does not deliver much notable improvement over whatever you are presently running. I guess my thought is that you can do better without having to spend more. I hope this answers to some degree my thoughts and confirms that I am not just spewing comments about a product line I have never experienced. This being said, my comments are based on the 640 as I have not listened specifically to the 840 (so perhaps I am way off base, but the 640 was previously highly regarded by "professional" reviewers.)