CD direct to amp vs active preamp

How many of you folks have ever tried running your digital source with a built in "high grade" volume control directly to your amp and compared that to the digital source feeding your active preamp and then the amp ? I am just curious as to the results and if you noticed any major differences. Obviously, we would have to add not only the preamp, but also another interconnect to make all of the connections. If you've done this "test" with a passive or buffered line section, feel free to join in. Sean
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