Hi Nick B,
I own a few CDs which are HDCD "encoded". To play them back you need a player which is capable to handle HDCD. The difference is subtile. I think that the skill, knowledge of the recording engineer and the care he took for the recording session are much more important. Many HDCD CDs were from Reference Recording and the engineer was Prof Johnson; they are great recordings. I also own one of Madeleine Peyroux - Dreamland which is spectacular and was awarded a Record to Die For by a Stereophile reviewer.
The best recordings which I have auditioned so far are from AIX Recordings Blu-ray in 7.1 Dolby TrueHD "stage" mix or their Audio DVD in 5.1 MLP. 2L Recordings from Norway also offers exceptional recodings (Blu-ray and SACD in multi-channels) where as AIX REcording you are with the musicians.
JC:
There were also a number, although not many, mainstream recordings done using the HDCD process. Back a few years ago my wife bought a "Bee-Gees" CD that was HDCD encoded and that is where I noticed the difference in the volume level.
