digital volume control vs preamp vol con

Could someone tell me the difference between a digital volume control on a cd player and volume control on an amp/preamp. Is one better than the other? Is there an audible difference?
Wadia digital output is much less"colored"than any preamp I ever heard. Their digital volume control is done extremely well.
Digital volume control occurs in the digital domain. It is done by truncating bits of information to reduce the output level. Analog volume control occurs after the D/A process and is done on the analog signal. Is one better than the other? It depends on several factors. The first is the matching of the digital pre (or cd-player) to the amplifiers. If you are typcially listening above the 65% point on the volume control, the truncated bits will be much fewer than say if you are listening below the 10% level. If you were listening at the 10% level for normal loudness, you would definitely have audible degredation from the truncated bits. If I'm not mistaken, Wadia has a system whereby you can set the max level so that it is properly matched to the amplifiers--perhaps a Wadia owner can expand on this. If this is correct, that's a smart way around part of the digital problem. In analog this problem does not exist. The D/A converts the full, non-truncated, signal and the analog volume then attenuates that analog signal. However, analog has it's own set of problems. Anything in the analog signal path will add some degree of noise. This used to be a problem with the pots used for analog volume control. At this time, that's a relatively small problem and has had many years of attention to get the noise down to a minimum. I own two pre-amps in the main system. One is a Levinson #380S, the other is an EAD Ovation. The EAD is for home theater, although I have auditioned it as a stand alone pre-amp (not that I was serious about using it that way--but I wanted to hear how good it was). For CDs (and HT use) the EAD is very good. When using the EAD on my system I generally have the volume at -25 (which would be at the 75% mark). I still feel as though I get a little more using the #380s as the volume control with this set-up--but it's very close--to the point that I'm not sure that the reason I prefer the 380s is that it creates a less sterile sound with more palpable imaging and soundstage (that sounds as bad as reviewer garble de guck). Now, if you ever use an analog source, then you don't want to go to a digital volume control, because that will just do an A/D then truncate bits and then D/A. I listen to a lot of vinyl, I for that reason I would never give up the analog volume control. Also, it might interest you that the Levinson #39 CD player does have a volume control so that it can be used directly with amplifiers, but the volume control is in the analog domain. I hope all of this is helpful--in the end it depends on how well digital volume control is executed and how well a digital volume control is mated to the amplifiers (to minimize the truncated bits), and whether or not you intend to use analog sources now or in the future.