I have a 851-C and love the player. While I have not compared it to the 651-C, I have had players with the Wolfson chip sets and prefer the Analogue Devices DAC's. Better overall resolution.
Cambridge Audio Azur 651C vs Azur 851C
I know the 851C has more features, but can anyone confirm after going from the 651C to the 851C that they experienced better sound? My concern are the DAC chips used. The 651C has the twin Wolfson WM8740 chips. My Hegel integrated amp has an AKM AK4490 in it and when I use my 651C as a transport and play through the Hegel DAC, I do not get the rich full sound I get when I use the DAC in the 651C and the analog inputs in the Hegel. Cambridge Audio switched to Analogue Devices AD1955 chips in the 851C. I would like to see if anyone has experience between the two. Was there an improvement?