Most digital domain volume controls " bitstrip" if not used in their top 70% of full volume. "Bitstripping is taking 16bit down to 14bit and also 12bit if the volume is too low. Thorsten Losech (Kuei Yang Wang) of AMR believes any attenuation in the digital domain DSD(rubbish) or Redbook strips bits, I think not, only below 70% is my experience.
http://www.diyhifi.org/forums/viewtopic.php?f=2&t=2921
All is not lost though if you get a cdp that you can set the max output IE 4v 2v or 1v there are a few dac’s or cdp’s that can do this, you should do some reading of reviews to find out which ones.
The Cary 303/200 can be set for 2v or 4v with a link inside and has a digital domain vc.
Also some older Wadia’s with digital domain vc can also be set for max output for 6 different levels with links.
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Cheers George