My final post, lads. I had some pals over today whose ears I trust, much younger than me, all with a mortgage-load of audio gear. It was easy to switch between the Oppo 103 straight-in to the Don Sach's preamp vs. run through the Channel Islands DAC. I provided the "ear lube" via a local micro-brew pub for the fellas and it was much appreciated by the feedback.
The conclusion is clear: On an A/B test, no listener was able to identify the difference in sound with or without the DAC in any consistent fashion. Often as not, a listener who thought he could perceive a difference, was surprised to learn that the DAC was out in the loop. I personally, switching the selector, might have perceived a 5% difference in improvement in the performance of my system with the DAC, but that might be my desire to validate my expenditure for the DAC. As I continue to perform this comparison after my pals left, I do think there is a maybe 5% improvement in the sound overall, with maybe a bit more clarity, but it is quite subtle.
So, the conclusion I have reached is that you have a pretty good DAC, or an Oppo upgraded by somebody (mine was upgraded by Stereo Dave and the upgrade was instantly apparent), the sonic value of a DAC in the sub-$1000 price range might be an expense of dubious value.
BTW, I upgraded pair of Mundorf Silver Oils output caps for Jupiter Copper caps in my preamp at the same time I hooked up the CIA DAC so that might have swayed my initial favorable impression the DAC. The Jupiters caps are a 10% improvement in the sound of the already excellent Don Sachs preamp -- by far the best I have heard in my system.
Cheers, Mark