The 600 (well, looking at the 640R) is a cinema amp and a quick look at reviews show what I found with previous CA amps and receivers, that they lack fine details especially at higher frequencies where music sounded more artificial than natural or neutral even.
Have you heard a NAD before? Definitely try one out in store as I think you'll be surprised.
The D 3020 outputs sound that rivals amps twice the price or more and has been highly reviewed all over and as many say, it carries the renowned "3020" name with a level of pride.
If you're happy with 2.1 then this would easily replace your Cambridge Audio and you can recoup some cost back by selling your old equipment. You'll also save a lot of workstation or desk space.