Their are enough real differences to make it a matter of choice.
The 840c 's balanced outs are very nice. Very, very quiet.
i use one of the DA inputs from my small dish and the other from my upsampling DVD player.
Go to CA site and read the 'blurb' ..... The differences may or may not make a difference to you. The '840 has some Anagram Technologies circuitry which is not offered on other models.
On a practical, experience note:: My '840c simply did NOT like the output from an Apple Airport Express. The APE has poor clocking and the CA player would sometimes loose lock. I am told the software update for the '840 'helps', but have not had the nerve to install. You need a Null Modem Serial cable for this and a computer with a serial port.
