My H/K AVR520 also has built-in HDCD decoding. I actually bought an HDCD sampler, and it has some of the same tracks in both 16-bit and HDCD to "show" the difference in HDCD. I can't for the life of me hear any difference between the HDCD and non-HDCD tracks, but some people do claim that HDCD is noticeably better than regular cd's. DVD-A is a much more noticeable improvement to me.