I have not listened to the 303/200 because that model wasn't available when I bought the 306/200. The 306/200 upsamples to 192KHz while the 303/200 does 96KHz. For me, one of the deciding factors was the ability to use the 306/200 as a DAC because it has Optical, Coaxial, and AES/EBU digital inputs. I route my 5-disc changer digital output through the 306/200 to take advantage of its DACs. Sounds great! There are several posts up on http://audioasylum.com about the Cary CD players.
Here are some photos and my comments on the 306/200:
http://mycollins.net/audio/caryadc.html
Here are some photos and my comments on the 306/200:
http://mycollins.net/audio/caryadc.html