I'm interested to know how the C542 and the new C515BEE compare to my C521BEE sound wise. Is the 542 a big upgrade over the 521? If so, in what ways? Is the 515BEE better than the 521BEE given that some of the technology is newer? WHF team - you gave the 521BEE 5 stars when it was current and have now given the 515BEE 5 stars. In what ways would you say they are different?