The most significant technical difference is that the current Cambridge 640C uses two Wolfson DACs verses the single DAC in the 540C. I reviewed both first versions of the two CDPs and the 640C V2 and compared them to some other popular budget HiFi CD players here: http://www.audioreview.com/cat/digital-sources/cd-players/cambridge-audio/PRD_299480_1586crx.aspx#review0.
I believe that the 540C V2 is much improved and gets excellent reviews by the Absolute Sound among other HiFi journals. The principle difference I hear is that the 640C V2 has better resolution across the frequency spectrum and provides more "space" around instruments and voices than the 540C. I own the 640C V2 and like it a lot.
I believe that the 540C V2 is much improved and gets excellent reviews by the Absolute Sound among other HiFi journals. The principle difference I hear is that the 640C V2 has better resolution across the frequency spectrum and provides more "space" around instruments and voices than the 540C. I own the 640C V2 and like it a lot.