I've heard both extensively. A well broken in Cambridge 840C is really hard to beat. The Cary 303/300 on the other hand just doesn't quite do it for me; of course a lot of it depends on which 12AU7 tubes you use. I think considering you are already using tubes in your preamp and power amps that you would definately prefer the Cambridge. Both the Cambridge 840C and Cary 303/300 are made in China.
Cambridge 840c vrs used Cary 303/300
I've been seriously considering the Cambridge 840c CDP. Many like the way it sounds after broken in. They sell used here almost every week. But, I've seen some good used buys on Audiogon for the Cary 303/300 CDP. I'm running with tubes in the preamp and amps. I like the build of the Cary model. Any comments of owners who are familiar with both would be appreciated. Either choice would be an improvement to my current CDP. Thanks!