20-bit, you say? I seem to recall a version of Astral Weeks (or Tupelo Honey?) that I bought was 20-bit.
I'll have to see if the Oppo says its HDCD.
So, do they sound any better?
The Joni Mitchell HDCDs do sound better than the old CD I had, so I think they were a better transfer from analogue to HDCD. There were a lot of 20bit remastered CDs released a few years back but they're just standard 16bit CDs. I would love the old Joni Mitchell CD4 Quads released on BDA, DVDA, or SACD.