Well, this is what I found out from the Oppo website:
Q: Does the OPPO DV-980H support HDCD?
A: Yes, the DV-980H fully supports HDCD. When a HDCD track or HDCD disc is played, the on screen display (OSD) will show "HDCD" briefly. When a standard CD track is played, the OSD will show "CD" briefly. HDCD decoding is done by the DV-980H if analog audio output is used. When digital audio output is in use, it is the responsibility of the AV receiver to decode the HDCD digital stream.
So, since I have my Oppo hooked up via HDMI, and the 1800 can't decode HDCD, I'm not getting the benefits of HDCD. I suppose I could hook it up via analog, but since I'm looking at a new receiver anyway, I might just get one that decodes HDCD.
By the way, my Oppo does bitstream DSD.