RW,
You are correct. The Oppos have remote controlled variable volume. However, I believe it is a digital domain volume control which drops bits in order to decrease the volume. Digital volume controls have generally been attributed with losing some amount of resolution once they are turned down more than a couple of steps from max.
I own an Oppo 970 with level 3 mods from EVS. It is a very good player all around and I do use it connected directly to my power amps using the built-in digital volume control. I haven't noticed any major sonic degradation when playing it a lower volume levels, but I do sometimes feel that it is giving up a bit of resolution at lower volumes.
I believe that the Cary uses an anolog domain volume control. Same with the Theta Miles, Quad 99 CDP and resolution Audio Opus 21 players that I also owned and used CD direct to amp. These units control volume in the analog domain, so they do not lose resolution as the volume is lowered.
Enjoy,
TIC