Cambridge Audio 540 vs. 640

What is the difference between the Cambridge Audio Azur 540 and 640 amp? I mean besides the w.p.c. ? Any audible difference?
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:
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 don't know. I really like Cambridge Audio gear (CD players especially), but I think their integrated amps miss the mark because they don't provide main amp in jacks like Bryston and NAD.